Geognosy & Geology

Introduction

The inanimate objects of our planet may be considered from two points of view, either in respect to their mathematical and physical properties, and chemical compositions, as individuals, or as forming parts of a whole, combined according to certain definite conditions.

The science which treats of the inorganic components of our earth, from the first point of view, is that of Mineralogy, or Anorganology, while Geology has reference to the second mode of their consideration. Like astronomy, geology affords most sublime and elevated subjects of contemplation; and like it also, it has made astonishing progress within the last few decades.

Geology is properly included under geography; since by the latter, in its wider sense, we must understand the entire physical history and structure of the globe.

Inanimate nature is presented to us under three points of view corresponding to the three conditions in which matter is aggregated: namely, as gaseous (the atmosphere), as liquid (the waters), and as solid (the land or solid portions). According to this difference in the aggregation of inorganic matter, we have the following divisions of geology:

1. Atmosphcerology, or Meteorology.
2. Hydrology.
3. Mineralogical Geology, or geology in its restricted sense.

Like every other branch of the philosophy of nature, geology (in the above limited meaning) may be treated of in two ways, descriptively and historically. Hence the further subdivision into the descriptive portion. Geognosy, and the historical portion, Geogeny, or Geology in its most narrow signification. Geognosy furnishes us with ascertained and established facts, upon which, as a foundation, the theoretical superstructure of geogeny is reared. Hence it is evident that a study of the former must precede that of the latter; since it is only by the combination and comparison of facts, that logical conclusions and satisfactory theories become possible. Geognosy might then be understood as the account of the present peculiarities of the solid parts of the earth; but when we remember that our knowledge of the earth extends only to exceedingly minute depths compared with her entire radius, it were more modest in us to define geognosy as the account of the earths crust. It is to mining operations, particularly, that we owe our knowledge of this portion of the earth: at least it was this branch of art that first led us to the knowledge of certain laws of her structure. It is, however, not the only means which has enabled us to become acquainted with the lower regions of the earth’s crust: we shall see subsequently, how certain conditions of stratification reveal to us structures and relations at depths which it might be impossible for us, otherwise, to ascertain. Just as geogeny requires geognosy as a necessary foundation, so does geognosy require mineralogy; since it is aggregations of simple minerals, either separately or in combination, that constitute the earth’s crust. It is not all mineral substances that are prominent in this respect, by far the greater number are not brought into view; it is proportionably very few that present themselves as important constituents of rocks. Of these few, some constitute entire formations singly; others form large masses, only in combination with each other, or with the preceding. These different combinations, as well as the simpler mineral forms, all constitute a whole, geognostically speaking, to which we give the name of rocks. It is thus evident, that a mineral may occur as a rock, but that every rock must not necessarily be a simple mineral. Just as a mineral is compounded of simple elements, these being combined according to the rules of chemical affinity, so minerals may be compounded into rocks; the force influencing them, however, is not chemical affinity, but cohesion. Furthermore, as the ingredients of mineral bodies stand, to a certain extent, in necessary combinations, this may only be incidental in regard to the constituents of rocks. These rocks may be considered in respect to their mineralogical composition, or with regard to the relation in which they stand to each other. The first brings them under the head of Petrography or Lithology, the latter under that of Oreography. Petrography treats of rocks in the minute, oreography in the great, or as constituting formations. The former bears somewhat the same relation to the latter, that mineralogy does to geognosy: the study of petrography must therefore precede that of oreography, in a philosophical examination of the entire subject.

From what has already been said, it follows that rocks may be divided into simple or homogeneous, and mixed or heterogeneous; yet, however distinct the two ideas may be, it is sometimes difficult to say, to which kind a certain rock must be referred. The compact varieties of the heterogeneous rocks sometimes present so intimate a mixture of ingredients, that at first sight they may not be seen in their true characters. The homogeneous are connected with the heterogeneous, by the most insensible transitions; as the heterogeneous are with each other. Thus what petrography loses in respect to the elementary variety of her forms, she more than makes up by the infinite diversity of their combinations.

There is no special difficulty in determining rocks when they present themselves in their characteristic forms; the proper appreciation of many transitions of one rock into another, can, however, in many cases, only be effected by means of the help afforded us by Oreography. It is, nevertheless, of the highest interest and importance to geologists to have an accurate knowledge of such transition forms, as they sometimes reveal to us very interesting affinities, or at least analogies between different formations.

As before remarked, only a few minerals occupy a prominent position in respect to geognosy; and the interesting generalization has been made that all such belong to the class of the oxygenids (the class characterized by oxygen combinations). These bodies, so important in geognosy, are the following:

1. Quartz, or crystallized silicic acid (silex), with the impure varieties, hornstone, silicious shale, jasper, and whetstone slate.
2. Mica, or micaceous bodies, with the nearly allied chlorite, and talc.
3. Feldspar, or feldspathic minerals (among which we distinguish feldspar proper or orthoclase), labradorite, saussurite, albite, and oligoclase.
4. Amphiboles, as hornblende.
5. Pyroxenes, as augite, diallage, and hypersthene.
6. Calcareous, including the pure and impure formations, limestone, marl, tufa, &c.
7. Dolomite, or carbonate of lime combined with carbonate of magnesia.
8. Gypsum, hydrated sulphate of lime.
9. Karstenite (anhydrite), anhydrous sulphate of lime.

General Petrography

The first part of geognosy or petrography teaches us the character of rocks or formations, and arranges them in systematic groups. Let us now turn our attention for a moment to this subject. Considering the rocks in a genetical point of view, they naturally fall under two heads; first, isonomic, or those which were produced by a simultaneous crystallization or deposition from an aqueous or igneous liquid; and secondly, heteronomic, those which are composed of materials evidently formed at different times, or in different localities. These appear to have been brought together by subsequent agencies, and their parts stand entirely in accidental combination.

All the parts of a rock, whether isonomic or heteronomic, must stand in actual combination. Considering the case of granite, which consists of a crystalline granular mixture of feldspar, quartz, and mica, we are enabled to assume that these three minerals, in actual combination, are the result of a simultaneous (not to take this term too literally) crystallization from a melted mass. Granite must therefore be counted among the isonomic formations. The same is the case with regard to syenite, the different, porphyries, &c. The expression simultaneous cannot be taken literally, since in the gradual cooling of the liquid matter of the different minerals, all could not crystallize at the same instant of time, owing to the difference in their points of congelation: one must harden first, and the other occupy its interstices. By simultaneously, therefore, we understand a certain period, during which the force of crystallization, or the congelation and separation of amorphous masses, was continually acting. Limestone, which in many cases is amorphous, is also to be counted among the isonomic rocks, since its formation was also brought about by a simultaneous deposition of its particles. The case is different with the heteronomic rocks, in which we must suppose one ingredient to have been completely formed before another was added to it, and forced by accidental agencies into a combination. Examples of heteronomic rocks are afforded by sandstone, grauwacke, and various other conglomerates. Conglomerates consist of two principal portions, one combining, and the other combined. The portion combined is that which we suppose to have been completely formed: it generally presents the appearance of fragments of different isonomic rocks, rounded by water into pebbles of various sizes. The combining portion is an earthy, finer substance, cementing the first into a compact mass. This is accordingly termed the cement. The following survey of the petrographical system will, it is hoped, serve to render the distinctions between isonomic and heteronomic rocks more intelligible, as well as to introduce the subject of Oreography, which is to be treated of subsequently.

Special Petrography

Isonomic Rocks

These present themselves to us under various conditions, and it is a matter of great interest to study the connexion between the different formation stages, and the probable or certain origin of rocks. With respect to the origin of many rocks we know little or nothing; as regards others, such as those which we see forming under our own eyes, we can speak with entire confidence. We need only refer to the lavas which burst forth as molten masses from the bowels of the earth, or to the different deposits from waters. Analogies, such as are of common occurrence, must furnish the key to those rocks with regard to whose formation we cannot speak with positive certainty. Take porphyry as an illustration, a rock in whose imperfectly crystalline, or entirely amorphous substance, we often find single crystallized particles, and even the most beautiful individual crystals. Analogies to this character are to be found in many processes of art. If melted glass be cooled very slowly, it is not a rare occurrence for single crystals to separate in the compact amorphous mass; and a similar phenomenon is observed in the slags produced in different metallurgical operations. The same is the case with respect to lavas in those parts of a lava current where a gradual cooling has taken place. When we find precisely the same circumstances in the older rocks, why may we not ascribe them to a similar, if not actually identical cause? When we see that during an exceedingly slow cooling of a vitreous slag, a crystalline granular solid is produced, possessing the same texture as many plutonic rocks, why are we not entitled to conclude that the latter have been produced in a similar manner?

The principal distinctions to be made, with respect to the variety of crystallization of isonomic rocks, are the perfectly crystalline, the semi-crystalline, and the imperfectly crystalline. These modifications occur both in homogeneous and heterogeneous rocks. In amorphism we distinguished the earthy, opaline, and vitreous. Genetically considered, the opaline bodies appear to have been produced by the gradual solidification of a gelatinous matter; the vitreous, by the rapid cooling of a melted mass.

Order 1st. Silicious Rocks

This order embraces the rocks in which silex forms the principal ingredient: we may divide it into three sections.

Section 1. Quartz Rocks; including:

Quartz rock proper; with its modifications, the compact, the granular, and the slaty quartz. Compact quartz rock is of a splintery fracture; the granular approximates closely to quartz sandstone, in fact it is difficult to draw the line of distinction. Here also belongs the silicious frit, which is nothing else than an incomplete melting together, or agglutination of quartz sand. It occurs in the vicinity of volcanic masses, to whose influence it owes its origin. The slaty texture of the last modification, the slaty quartz rock, is to be ascribed to mica, whose crystalline laminae, lying in the same plane successively, thus permit a separation. The remarkable part performed by the mica, in this way, will be referred to more fully hereafter, many rocks deriving from it the property of splitting in definite directions. When quartz rock, which is generally of a light color, acquires a darker tint by the addition of oxyde of iron and manganese, aluminous matter, &c., it passes into:

Argillaceous quartz rock, to which also belongs silicious slate, a combination of crystalline and amorphous silex, with clay slate. This is distinguished into a common, with splintery, and a jaspery, with conchoidal fracture. Its color is generally black, although sometimes occurring grey, green, or brown. It frequently contains anthracite, and it is to carbon in this form that silicious slate probably owes its black color. Silex traverses it in veins, always of a white color, the carbon of the rock never penetrating these veins. Calcareous spar also occurs in veins in a similar manner.

Jasper. This is an intimate combination of silex with a little alumina: generally colored brown by iron. It rarely occupies an extended place among rocks, being quite restricted in its occurrence. It sometimes incloses crystals of feldspar, in which case it becomes porphyritic. It passes into whetstone, and silicious shale. It has frequently a strong resemblance to a burnt clay in the so called porcelain jasper, a clay baked by igneous action. The banded jasper is a variety exhibiting layers of different color.

Section 2. Hornstone.

The rocks belonging under this head consist of an intimate combination of quartz and compact feldspar. The principal of these is the hornstone rock, whose most remarkable transitions are into quartz rock, and a compact feldspar rock called whitestone. An increase in the quantity of the quartz carries it into the former; a diminution of quartz, into the latter. The quartz is generally the common splintery kind, rarely waxy; the feldspathic material is more compact, rarely sparry. The predominating color is grey of various shades.

Section 3. Silicious Porphyry.

Silicious porphyry, as the name indicates, is a silicious mass, in which feldspathic crystals are interspersed. The principal varieties are:

Quartz Porphyry; of rare occurrence, and only found in Sweden. The general color is white, as are also the crystals of feldspar.

Hornstone Porphyry. This is often very similar to the preceding, but readily distinguishable by a simple blowpipe test. While quartz porphyry forms only a frit in the blowpipe flame, this melts, without much difficulty, into a white enamel. Its colors are grey, brown, yellowish; and in the mass thus constituted, crystals of feldspar are readily distinguishable.

Silicious Porphyritic-slate. This beautiful rock is rather rare. In masses of jaspery, silicious slate, lie feldspathic crystals of a light color. This rock readily passes into hornstone.

Jaspery Porphyry. This consists of feldspar crystals lying in a matrix of earthy jasper; and is of a lavender blue, grey, and greenish color.

Order 2. Micaceous Rocks

The rocks of this order derive their name from containing mica, or chlorite and talc, which are closely allied to mica. Chlorite and talc may either replace or accompany mica. In the first series (the micas), mica and its allies occur pure and distinct.

Section 1. Micas.

Mica. It is principally the biaxial mica that occurs as a rock; the uni-axial being but rarely met with. It is a little remarkable, that where mica occurs in very large quantity, the laminæ are never of very large size. It splits up into very thin plates, these consisting of minute scales of mica combined into layers. Its color is generally brown running into black, rarely silvery white.

Chlorite. This is met with under different forms, namely, as chlorite slate, as chlorite rock, and as potstone.

Chlorite slate is the well known schistose chlorite of the mineralogist Its colors are seldom lively, passing from dark-green into greenish-grey. Chlorite rock is represented by common chlorite, which is generally coarsely slaty, and readily passes into potstone, which is an intimate combination of chlorite and talc. This potstone is not unimportant in a technical point of view, serving not only as a material for the most important utensils of some nations, but also admitting of conversion into various shapes by the art of the turner.

Talc. The talcose slate of mineralogists generally exhibits a green, yellow, or white color. It passes, on the one hand, into chlorite and talc on the other, into steatite.

Section 2. Clay Slate.

The rocks of this section present an intimate union of talc, mica, or chlorite, with quartz and feldspar. The micaceous minerals predominate; and mica slate, a combination of the common biaxial mica with quartz, is the rock of this series which is most abundant. Those modifications which contain chlorite and talc occur but rarely.

Clay Slate. This tends towards chlorite, towards mica, and towards talc, in proportion as it contains a superabundance of any one of these three substances. Its laminated structure is very distinct, and there are few rocks which are as well calculated for a satisfactory study of all the laws of lamination as this. Large plane tabular, and very thin layers, which often traverse whole mountain masses, alternate with those of the most remarkable complication of folding and contortion.

The common clay slate, containing mica in superabundance, and of a grey color, often contains carbonaceous matter, which imparts a black color; oxyde of iron communicates a red, or reddish-brown tint. When the materials are very intimately combined, only a feeble glimmering will be observed; when this combination is less thorough, the scales of mica will be very evident on the surface of thin laminae, and produce some lustre. Chlorite slate betrays itself by its greenish color, communicated by the chlorite. A calcareous variety is of a clear yellow, blue, or greenish-white color, often covered by a ferruginous tinge.

The transitions of clay slate are very various: the principal are into whetstone, silicious, and grauwacke slate, and hearthstone.

Roofing Slate. This is nothing more than clay slate penetrated by carbonaceous or bituminous particles. The principal external peculiarities exhibited by clay slate are found in this variety also. When exposed for a long time to the air, it becomes covered with a white crust, caused by the disappearance of the carbonaceous matter. The rock is very lustrous on the planes of lamination. Nearly allied to it is—

Graphite Slate, an intimate mixture of clay slate with graphite. It possesses a metallic shining lustre, caused by the graphite contained in it in plates.

Alum Slate. This is an intimate combination of clay slate with iron pyrites, thoroughly penetrated by coaly or bituminous matters. From the former it derives a black, from the latter a brown color. The brown varieties burn with a flame. Alum slate is a substance not without its importance in the arts, as it furnishes, in a great measure, much of the material for the fabrication of alum. The iron pyrites contained in it undergoes oxydation, owing to the fine and divided state in which it occurs. Both the iron and the sulphur of the pyrites combining with oxygen, a sulphate of iron or green vitriol is formed. This is decomposed again, and the sulphuric acid combines with the alumina and potassa of the alum slate, forming alum. For this reason, that portion of the bed of alum slate exposed to the atmosphere, soon becomes coated with a white crust, which consists of coarse alum. Bituminous alum shale is especially adapted to the manufacture of alum, as it not only furnishes as good a material as the black, but from its combustibility may be used for fuel.

Calcareous Clay Slate, an intimate admixture of carbonate of lime and clay slate. It is a valuable rock, furnishing excellent materials for soils. While common clay slate does not act very favorably on vegetation, this variety permits the finest forest growth. It is of a dark color, for which reason it is put to a very peculiar use in some countries. This consists in sprinkling it, when crumbled into pieces, on snow-covered ground, thus accelerating the melting of the snow, at the same time that an useful manure is added to the soil.

Section 3. Horn Slate (Hornschiefer).

This section contains only one rock, horn slate. It is a tough solid substance, and is often a great hindrance in mining. Hornblende often enters into the more usual combination of mica and quartz, and communicates to the usual grey or dusky black color, a tinge of green.

Section 4. Flagstone (Gestellstein).

These are rocks consisting of a crystalline schistose mixture of micaceous minerals with quartz. First to be mentioned is:

Flagstone. In the mixture just referred to, mica is the prevailing component; chlorite and talc occur more rarely. As any one of these three mineral substances occurs combined with quartz, we have micaceous, chloritic, and talcose flagstone. The lamination of flagstone is very distinct. The quartz granules are generally invisible, being concealed by the mica. These quartz grains often occur in lumps, and form entire beds by their combinations; the micaceous matter investing these lumps produces a knotty undulating lamination. The color of the rock depends on that of the mica. The chlorite flagstones are generally green, the talcose, white.

Hornblende-, graphite-, marble-, dolomite-flagstone, schorl- and micaceous-iron slate, are rocks belonging in this place: they are distinguished from each other by the proportion in which one or other of the above-mentioned ingredients enters into its composition; this taking place frequently in such quantity, that the micaceous substance is entirely displaced.

Section 5. Gneiss.

This section is composed of rocks which consist of micaceous substances, quartz, and feldspar, and possess a decidedly crystalline laminated structure. The first species to be mentioned, is

Common Gneiss. The mica is arranged in parallel layers, imparting to the rock its schistose structure; color grey, brown, and black: the quartz is generally grey, and in no great proportion, and is even sometimes entirely wanting. The colors of the feldspar are mostly grey and white, the red is rare. Similar modifications are found in gneiss to those in flagstone, effected by the micaceous element. Thus we have a chlorite, or a talc gneiss, as chlorite, or talc, replaces the mica. On account of the solidity of gneiss, it is much used for building and other similar purposes. Hornblende is sometimes added to the other constituents of gneiss, thus producing hornblende-gneiss. The micaceous element is sometimes entirely displaced by the hornblende.

Order 3. Feldspathic Rocks

Feldspathic minerals form the constituents of these rocks. Common feldspar itself, or orthoclase, most generally constitutes this ingredient; in rarer cases, the vitreous feldspar or sunadin, as also the compact feldspar. These feldspathic substances may be replaced by their allies, albite and oligoclase. Quartz and mica are generally united with feldspar, sometimes so intimately that the mixture can scarcely be distinguished from a chemical combination.

Section 1. Granite.

Granite, that well known and important rock, is a mixture of feldspathic and micaceous minerals with quartz. It is one of the most interesting rocks, both on account of the great number of its modifications, and the wide extent to which it prevails. Its color is very variable, depending upon whether the predominant feldspathic matter be flesh-color, greyish-white, or greenish; the quartz transparent, milk-white, grey, rose-red, or sapphire; the micaceous matter brown or silver white; or whether the mica be replaced by chlorite or talc. The two latter minerals often occur combined, forming what is distinguished by many geologists as protogine. Granite has the same general composition as gneiss, feldspar predominating in the former, mica in the latter. The principal difference lies in their different modes of occurrence; and genetically considered, the two rocks have an entirely different formation. Gneiss has always a decided lamination or stratification, which is rarely seen in granite, and then in an entirely different manner. The grain of granite is present under all its modifications; it may be large and coarse, or small and finely granular; and while in the latter the different minerals can no longer be distinguished by the naked eye, in the former each constituent particle appears to occupy an almost independent position. In the coarse-grained granite, the mica, for instance, is sometimes found in plates which are more than a foot square. Granite is especially favorable to cultivation: decomposing readily, it furnishes many inorganic matters of vast importance. Feldspar, in whatever combination it may be met with, readily decomposes under the influence of water, heat, &c., and after single soluble constituents have been removed, it then forms kaolin or porcelain clay. Granite is a very valuable building material, and is of importance in the manufacture of porcelain and glass.

Syenite. This may be considered as a granite, in which hornblende occupies the place of mica. For this reason it is sometimes called hornblende-granite. Mount Sinai, a name associated with all the traditions of our faith, is composed of this rock; on which account the name sinaite has not inaptly been suggested for it. Like granite, it is often found porphyritic. If the hornblende, or its homologue, disappear, we have a rock called granitelle. The occurrence of mica in this, appears to be a superfluous, not necessary constituent.

Section 2. Whitestone (Weisstein).

This is characterized by compact feldspar, or albite, and the homologous species. The whitestone, properly speaking, is a mixture of compact feldspar and quartz. The fracture is splintery; the colors greyish, yellowish, and greenish- white. Compact feldspar, or albite, is indeed characteristic of the whitestone; but where this passes into granite, or approximates to it, it assumes a more or less sparry or granular texture. Mica occurs as an additional component, and may be recognised by its dark color, as also by the lamination which it produces. A variety in which grains of quartz and laminae of mica can be distinguished, appears similar to several fine-grained modifications of granite, and has received the name of granulite. Crystals of feldspar, interspersed in the mass, give it a porphyritic appearance.

Eurite Porphyry. Under this head are to be found some of those red and black porphyries, termed quartzose. It is a porphyritic mixture of compact feldspar or adinole, with feldspar, albite, or an allied mineral. The colors are dirty flesh-color, running into green, and greyish white.

Clay stone porphyry (porphyre terreux), a porphyritic mixture of a substance consisting of compact claystone, of an earthy fracture. It is not nearly so hard as eurite porphyry. The presence of silex imparts considerable firmness to it. Claystone porphyry is of a dirty flesh, violet, grey, and light color. Feldspar is separated either in distinct crystalline particles, or in indefinite angular fragments, in which latter case it forms a porphyroid.

Section 3. Trachytes.

This section includes rocks which contain vitreous feldspar (sunadin) as the principal constituent; the feldspar in most cases, even when recently laid bare, appearing as if it had been exposed to the weather. The rocks of this section are all of igneous origin.

Trachyte (trap porphyry, domite, feldspar lava). In this rock sunadin predominates, and as it often forms an aggregation of prismatic crystals, trachyte is very porous, and rough to the touch. The fresher the feldspar, and the greater its proportion, the more lustrous is the rock. A peculiar substance, termed andesin (most nearly allied to oligoclase), often replaces the feldspar, in that case forming the andesite of many geologists. Mica and basaltic hornblende are often contained in it, as also albite, which minerals modify the rock in various ways. Oxyde of iron frequently imparts a ferruginous tint, otherwise it is of a light color. A crystalline granular trachyte is distinguished from trachytic porphyry, porphyroidal trachyte, and scoriaceous trachyte.

The first of the above-mentioned rocks is a crystalline granular aggregation of feldspathic crystals, and in Italy, where it occurs very abundantly, is called saffbmorto, or necrolite. Trachytic porphyry often contains feldspar in beautifully perfect crystals of different sizes. They lie in a matrix which appears more or less decomposed. Porphyroidal trachyte, instead of crystals of feldspar, contains only undefined angular fragments of feldspar. Scoriaceous trachyte derives its name from its appearance.

Clinkstone (phonolite, porphyry-slate). The petrographical constitution of this rock is but little known. What we do know is, that it consists of an intimate combination of feldspar with an unknown body, which, in many cases, appears to be a zeolitic mineral; this union being sometimes so perfect as to give it the appearance of a simple mineral. Silex often communicates to it an extraordinary degree of hardness. A grey color is peculiar to it. It is often porphyritic, with crystalline glassy feldspar disseminated in its substance. The minerals generally included are mesotype, natrolite, chabazite, and apophyllite.

Section 4. Obsidian.

In rocks of this section the feldspar has been entirely fused, and only occasionally exhibits a crystalline structure. The action of fire is readily recognised, for which reason these rocks have more or less the appearance of glass.

Pitchstone. This is of imperfect conchoidal fracture, of waxy lustre, and of grey, green, red, brown, and black color.

Pearlstone is characterized by its granular or concentric lamination, and by its vitreous lustre, passing into iridescence. Its colors are grey, yellowish red, and brown.

Obsidian occurs, like all the rocks of this section, in volcanic regions. It is characterized by its striking conchoidal fracture and perfect glassy lustre. The broken fragments have very sharp edges, and strikingly resemble a dark colored glass. Its black and brown colors depend on carbonaceous substances, for which reason obsidian yields a white result before the blowpipe, by which it is distinguished from many slag-like rocks.

Pumice, or Bimstein. This is nearly allied to obsidian, and differs only in its condition of aggregation. While the former is perfectly glassy, this has a more or less perfect glass-like cellular spongiform texture. It is found in all stages of the spongy scoriaceous character, running finally into obsidian. Its economical applications are well known.

The rocks of this section frequently have their feldspar separated, and then occur as true porphyries.

Order 4. Pyroxene Rocks

The rocks of this order are characterized by pyroxene minerals, particularly malacolite, augite, diallage, and hypersthene.

Section 1. Pyroxenes.

Only one species occurs under this head, pyroxene rock proper. This is a granular foliated mixture of malacolite with augite, and is of an oil or olive green color.

Section 2. Leucitophyre.

This section includes rocks consisting of leucite and augite. The mixture occurs in various degrees of perfection.

Leucitophyre (leucomelan). This exhibits a great number of modifications depending on its structure. The crystalline granular form (also called leucite lava) contains leucite and augite in crystalline grains plainly distinguishable with the naked eye. When the mixture is more intimate, the dark rock appears sprinkled with white. The porphyritic (dotted) lava is an indistinct mixture of uneven earthy fracture, in which lie crystals either of leucite or augite, or both. The compact leucitophyre is often very similar to basalt. The vesicular, slag-like, spongy, and glassy kinds, are sufficiently characterized by their names. The products of atmospheric decomposition proceeding from these rocks, are very favorable to vegetation; some varieties, as the slaggy, however, resist such influence most energetically. In places where this kind exists, as in volcanic or igneous regions, extensive tracts of land are barren and desolate. It is almost impossible even for cryptogamia to extract any inorganic nutriment from this durable rock.

Section 3. Basalts.

This includes several intimate combinations in which augite predominates, sometimes, however, replaced by basaltic hornblende. Magnetic oxyde of iron is usually associated with the augite, existing sometimes in a separate crystalline form. As the mixture of the constituents of basalt is so intimate, it is necessary to direct our attention to surfaces which have been acted upon by the weather. These plainly indicate the existence of labradorite, sometimes replaced by a zeolitic mineral. Olivine (common chrysolite) is an extra ingredient, but is so generally found in basalt, as to be considered an essential constituent by some geologists.

Basalt. This exhibits various diversities in respect to its state of aggregation, these being quite analogous to those which we have considered in rocks of undoubted igneous origin, as in leucitophyre; the names of the varieties, compact, earthy, vesicular, slaggy, spongy, and glassy, sufficiently indicate their distinguishing characters. This rock is of a very dark color.

Amygdaloidal Basalt. This is a variety of basalt in which occur spherical, ellipsoidal, and irregularly shaped cavities, generally filled or lined with crystallized or crystalline minerals, which are mostly zeolitic.

Section 4. Dolerites.

This section comes very near to that of the basalts. It embraces mixtures of augite with feldspathic and ferruginous minerals; among the latter magnetic oxyde of iron and specular iron are in a more or less crystalline condition.

Dolerite (basaltic greenstone). Augite, generally the predominant component, exerts the greatest influence on the character of dolerite. Its dark color depends on augite, being varied to lighter by feldspathic substances (especially labradorite). Some one or other ferruginous mineral appears always to be present. This exerts a great influence on the color of the rock; in the ochrey condition it penetrates the mass, and colors it reddish-brown. The components of dolerite are generally distinguishable; there is, however, a modification, exhibiting a less degree of crystallization, and forming an insensible transition into basalt; this is known as anamesite. Dolerite is exhibited as crystalline, granular, porphyritic, vesicular, or slaggy (as in dolerite lava).

Section 5. Trap Rocks.

The term trap was formerly made to embrace many species essentially different. It is therefore a matter of some doubt to which the name shall be applied in restricting the appellation. The name is derived from a species of rock which forms a cap on the Scandinavian Trapp-berg, elevated in a terraced or step-like manner. This rock is now assumed as the typical trap. It is a mixture of augite and some feldspathic mineral, generally labradorite, or its compact variety, saussurite.

Trap Proper. This rock varies in respect to the distinctness of its ingredients, and is of a very dark color, owing to the augite. When oxyde of iron pervades the mass it imparts a brownish shade. It occurs porphyritic, granular, and compact. Trap porphyry, which contains crystalline labradorite or feldspar in the trap mass, is sometimes called melaphyre.

Amygdaloidal Trap is a compact trap, with cavities containing various minerals. The principal of these are either silicious, as amethyst, chalcedony, opal, &c, or zeolitic, as mesotype, stilbite, desmine, apophyllite, harmatome, &c.; likewise, calcareous spar, spathic iron, and brown iron ore. The occurrence of manganese ore is of especial economical importance.

Section 6. Diabase.

The mineral predominating in these rocks is hypersthene, which occurs in combination with some feldspathic material, as labradorite, albite, and with chlorite. The amount of labradorite is not inconsiderable, yet it has not as much influence on the color as the chlorite. This color is green with the latter mineral. Diabase mixtures exhibit a tendency to intimate combination, on which account the crystalline structure disappears more or less, and this in proportion to the extent to which the earthy chlorite is distributed in the rock.

Diabase Proper (greenstone), which is of a granular porphyritic and compact character, is very hard and difficult to break; the color is dark in proportion as it contains hypersthene, or augite, and chlorite.

Greenstone Porphyry is an intimate diabase combination from which sparry or compact feldspar, labradorite, saussurite, or oligoclase, is separated.

Variolite. A diabase of a dark color, with roundish light particles, included.

Amygdaloidal Diabase. This is a fine grained diabase in which lie amygdaloidal, or undefined masses of brown spar, or calc spar. Variolite (Blatterstein) is, on the whole, a compact rock of an earthy fracture. Its colors vary between green, grey, brown, and black; the first of these predominates. Genetically, considered the rock seems to have acquired the amygdaloidal character by the influence of vapor, ascending gaseous bubbles leaving cavities which were subsequently filled by infiltration. The slaty diabase amygdaloid or tabular spar, distinguished from the preceding by its laminated texture, presents other marks contributing essentially to its specific character. In its green or brown mass there lie spheroids which are frequently flattened. In this case the flattened sides lie parallel to the planes of stratification. Chlorite may occur separated like calc or brown spar. The calc spar passes into compact limestone, which then forms beds alternating with the tabular spar. Oxyde of iron sometimes penetrates the rock in considerable quantity, forming a poor ironstone. The presence of much talc gives it a soapy feel.

Section 7. Hypersthene.

Under this head, which includes rocks in which hypersthene is mixed with feldspar, or some allied mineral, are especially distinguished:

Hypersthene rock. This is a crystalline granular aggregation of labradorite or saussurite with hypersthene. The latter exerts the greatest influence on the rock, often occurring in so great quantity that the feldspathic mineral is entirely removed. Hypersthene rock is therefore of a dark color, and resists in a remarkable degree the action of the weather. The addition of chlorite converts it into diabase, and when diallage enters into combination it becomes euphotide.

Section 8. The Euphotides.

In these rocks diallage is combined with labradorite or saussurite.

Euphotide (gabbro, granitone). This is a crystalline granular combination of the above-mentioned minerals. Diallage is generally the prevailing constituent of this exceedingly hard rock. The color is that of diallage, an undefined grey passing into brown. Hypersthene and some other minerals are often added. It passes into hypersthene rock, more rarely into the rocks of the following order; it resists, almost entirely, the decomposing action of the atmosphere.

Order 5. Rocks of Schiller Spar

Schiller spar or metalloidal diallage, which is a well known mineral, is also entitled to a place among rocks. It is either pure, or mixed with saussurite. Should the latter be the case, it is often variolitic, the saussurite being separated in round particles surrounded by schiller spar. In porphyritic schiller rock, distinct crystalline foliated masses of schiller spar occur. Common schiller rock (primitive greenstone) often alternates with serpentine, and in fact bears a considerable resemblance to it. It is either pure compact schiller spar, or else mixed with a little saussurite.

Order 6. Serpentine Rocks

The rocks of this order contain serpentine as their characteristic constituent.

Serpentine Rock. Serpentine, like schiller spar, ranks both as a mineral species and as a rock. It is principally common serpentine that occurs in the latter condition, the precious and fibrous being restricted to small portions of its mass. Green is its peculiar color; the different shades, other than this, depend on the presence of foreign substances. It is exceedingly rich in foreign species, among which asbestos, pyrope, magnetic oxyde of iron, &c., are the most conspicuous.

Ophite. This rock, so much used, especially for purposes of art, is a mixture of serpentine and compact limestone. The limestone is often separated as marble, and veins colored by different substances give it a very beautiful appearance; verd antique marble is here included.

Order 7. Amphibolic Rocks

Minerals of amphibolic character, as grammatite, actinolite, asbestos, anthophyllite, hornblende, &c, form the predominant ingredients in rocks of this order. It is hornblende, however, either pure or in combination with other bodies, which forms the mass of the rock.

Hornblende rock is nothing more than hornblende in a pure state, or with a few unimportant additions. Two kinds of this rock are distinguished: hornblende-rock proper, and hornblende-slate. The former is crystalline granular, and less hard than tough. It is therefore difficult to break or blast, and forms a considerable impediment in the way of mining or excavating. Hornblende-slate, which consists of scaly hornblende, possesses a rather imperfect stratification, with the same greenish-black color as the last. Actinolite and anthophyllite occur in both varieties, as unessential ingredients. Other minerals also occur, and cause the transition and hornblende flagging-stone, hornblende gneiss, syenite, diorite, &c.

Diorite (greenstone). This rock was formerly considered to stand in such a relation to diabase, as to be entitled to consideration only as a variety of the latter. The more careful investigations of Hausmann have, however, shown that they are essentially different. While the former contains a pyroxene mineral, hypersthene, as the predominating constituent, in combination with a feldspathic, as labradorite, or albite, and chlorite, the latter (diorite) is a more or less distinct mixture of an amphiboloid substance, hornblende, with albite. It is, in composition, nearly allied to syenite. The hornblende imparts to it a dark greenish-black color. The difference in the manner in which the combination of the constituents takes place, permits a distinction into: granular diorite, whose particles are crystalline granular; globular diorite, in which its granules are enveloped by concentric coats of compact feldspar, or a variety of hornblende; porphyritic diorite, where albite is interspersed in the mass; and compact diorite (aphanite) consisting of a very intimate mixture of the above-mentioned minerals. Both the diorite and hornblende rocks are capable of withstanding the action of the atmosphere to a very high degree. The feldspathic matter weathers first, and gives rise to a very rough surface, well calculated for the abode of various cryptogamous plants. Umbilicaricae. for instance, occur in such localities in great perfection and profusion.

Order 8. Calcareous Rocks (Limestones)

The carbonate of lime of mineralogy, either pure or combined with other substances, is an exceedingly important constituent of the earth’s crust. There is, perhaps, no other to be compared with it in this respect. It not only forms immense masses in particular localities, but is universally distributed, this being the case both with respect to the pure varieties and to the mixed.

Section 1. Limestone Proper.

This section includes all rocks composed of pure carbonate of lime. The principal modifications are:

Marble, or pure carbonate of lime in a crystalline granular state of aggregation. The name of marble is often applied, vulgarly, to rocks which are not entitled to it. It is not upon the markings of a limestone, whether close-grained or crystalline, that the title of marble, geologically speaking, is based, but simply upon the condition of aggregation. A marble may, and indeed often does, have various kinds of coloration or other markings, but then it is not every limestone thus marked that is a marble. The markings often depend upon the penetration of the limestone by other matters. Common marble is pretty generally distributed in various degrees of fineness and purity. The hardness varies considerably, one extreme being as conspicuous as the other. The use of marble in building and sculpture is well known. The white variety, as it occurs near Carrara, in the Appenines, in the island of Paros, and in Mount Pentelicus in Attica, is the most esteemed. This is not so frequent as the yellow, greenish, grey, and bluish modifications. It sometimes appears black, and then passes into anthraconite. The presence of various colors imparts a spotted, pitted, or veined appearance. Marble contains various incidental ingredients which sometimes cause it to deteriorate in value. Iron pyrites is sometimes so intimately combined as to escape detection. Under the influence of the atmosphere a hydrated oxyde of iron is formed, which imparts a brown color to the surface. Hence it is that many columns or structures of marble become coated with a yellowish tinge. Augite, schorl, feldspar, hornblende, mica, &c., are also frequently met with, and have given rise to the separation of various rock species, which, on account of their limited occurrence, are not generally recognised. This is the case, for instance, with the feldspathic, pyroxenic, pyropian, amphibolic, and cipolin calciphyre of A. Brogniart.

Breccia Marble is a, combination of angular fragments of marble by a calcareous cement. The two portions are generally of a different color.

A weathering of marble is out of the question, as the atmosphere is incapable of causing the decomposition of carbonate of lime. A crumbling away of the jock may, however, be effected by the decomposition of the interspersed suiphuret of iron, and of the carbonates of metals, causing a necessary swelling of particular portions at the expense of others.

Compact Limestone. This form of calcareous matter is the most important, in a geognostical point of view, and embraces a large number of varieties.

The common compact limestone possesses, on a large scale, a conchoidal, on a small, a splintery fracture. It is mixed more or less with other substances, especially with particles of clay, which cause a diminution of hardness, and silicious particles, which cause ar. increase of hardness. The degrees of hardness are very different, as also the colors, which white, through grey, bluish, and reddish, into black. Different colors sometimes co-exist, similar to what is seen in marble, and produced by like causes. Carbonates of iron and manga riot uncommon constituents, which impart to the stone, when long exposed to the weather, a farraginous or brown crust.

Limestone shale is distinguished by its rine lamination, rather thick than thin, however, and by its extraordinarily rine grain. It is important: use in lithography. Its principal locality is at Solnhofen from Pappenheïm.

The other varieties, the breceious limestone, the columnar, mamillary, the cavernous, and the cellular limestones, are sufficiently well characterized by the names. The cellular is of a marly character, traversed in various directions by a purer mass, which is often calcareous spar, thus producing the cellular charad wr roestone. is an aggregation globules of compact limestone, from the size of a pea (when it is sometimes called pisolite) down to very minute particles, the individual particles often cohering with extraordinary firmness.

Calcareous Tufa (travertine). This more or less porous rock, on account of its lightness and facility of working, affords an excellent building material. The pores depend partly on organic matters, which it incloses, and partly they are stices left throughout the aggregating material. It is frequently colored yellow or brown by oxyde of iron or manganese: white, however generally predominates.

Scaly Limestone, or limestone with a scaly lamination, is produced by hot calcareous springs. It occurs at Carlsbad, and other places.

Chalk is carbonate of lime in an earthy condition.

Tripoli (rotten stone). Combination of silex and alumina with lime. Light, earthy, stains paper yellowish or greyish-white.

Marl consists of clay with limestone, and has an earthy, somewhat plane fracture. Colors greyish.

Section 2. Silicious Limestones.

This comprehends limestones with a greater or less proportion of silex.

Porous Limestone occurs in nature as compact and granular. It is rough to the touch, and has the peculiarity of soaking in water greedily, without giving afterwards any indication of its presence.

Silicious Limestone (conite) possesses a variable proportion of silex, and is without the property exhibited by the preceding species with respect to water.

Chalk Rock. Limestone with a good deal o\ silex. a little clay, and some carbonate of iron. It is important in a technical sense, owing to its property of hardening under water, and hence well adapted for submerged walls.

Section 3. Marls.

These rocks are composed of carbonate of lime with clay, probably not in chemical combination. Lime predominates. Marl forms masses which are either slaty or indefinitely shelly. The lamination of the rock is very decided, causing it to fall to pieces readily.

Lime Marl. Nature has drawn no lines between the different kinds of marl. The species can be determined only approximately by the prevailing component. An artificial limit has been set between them. According to this, lime marl, of which there are the varieties, marly limestone, marly lime slate, and marly earth, must contain over seventy-five per cent, of carbonate of lime. When it contains between seventy-five and fifty per cent., it is called clay marl. This occurs in not inconsiderable masses; and in an agricultural point of view is as important as the marls in general. The color and hardness vary considerably, the former being greyish, yellowish, reddish, greenish, and white. The grey and black colors are due to bituminous particles, the green to chlorite. Clay marl is not decomposed, but crumbles to pieces readily; water penetrating between the laminæ and into the pores by capillarity, experiences an expansion by heat or freezing, which splits the rock into fragments.

Fetid Marl. Marl often contains so much bitumen as not only to be colored brown or black, but to emit a strong odor when struck. The outer coating is frequently white, the effect of evaporation or abstraction of the bituminous particles. Fetid marl rock is distinguished from fetid marl slate and fetid marl earth. The three varieties are only defined by their external appearance. The fetid marl slate, also called bituminous marl slate, is in many places entirely impregnated with copper ores; on which account it is in many places mined and worked for copper, notwithstanding that it generally contains only three per cent, of the metal. The bitumen which penetrates the rock is often separated in a pure state, and singularly enough, principally in places where there are organic remains; so that the supposition that the bitumen depends upon such remains, and is nothing else than a product of decomposition of organic matter, seems to be not entirely without foundation.

Section 4. Fetid Limestone

Embraces those limestones that are so transformed by coaly or bituminous substances, as to possess a dark color, and to diffuse a bituminous odor when struck.

Fetid Lime, or bituminous limestone. It is divided into fetid lime, fetid clay, oolitic fetid lime, breccious, and porous or cellular. The more bitumen the rock contains, the darker are its colors, which are generally grey, brown, or brownish-black. Those portions exposed to the air are generally lighter, often entirely white, the inside remaining dark. This is caused by the passing off of the bitumen leaving the rock somewhat porous. The bitumen is often separated as asphaltum. The rock is often penetrated by other foreign matters. Thus there is frequently a fetid quartz corresponding with the rock crystal in pure limestone.

Anthraconite, or carbonate of lime with a considerable amount of carbonaceous matter. This occurs compact and scaly granular. Threads of white limestone, or brownspar, often run through it.

Order 9. Magnesian Limestones

The rocks constituting this order consist of magnesian matter, or of a combination of carbonate of lime with carbonate of magnesia.

Magnesian limestone is the purer combination of the two above-mentioned substances, and is divided into dolomite and compact magnesian limestone. Dolomite bears the same relation to the other rocks of this order, that marble does to the limestones: the crystalline granular structure is characteristic of it. Its colors are exceedingly varied, as also its degree of hardness. White predominates; the tint may, however, be blue, grey, yellow, or ferruginous (from oxyde of iron). It abounds in foreign ingredients, on which account it is not unimportant to the mineralogist. The compact variety possesses a brittle, flat, conchoidal fracture, and is generally harder than compact limestone.

Fetid Magnesian Limestone contains a portion of bitumen, which imparts a dark color, frequently modified by oxyde of iron. The crystalline granular, which is either scaly or an aggregation of magnesian rhombohedrons, has a rough appearance, and an iridescent lustre on the crystalline particles. Other varieties are the compact, breccious, cellular, porous, and earthy.

Magnesian Marl. This is a very impure magnesia, containing, in addition to the usual magnesian combinations, carbonate of iron or manganese, alumina, and silex. The fracture is earthy and uneven. When fresh it is of a grey or bluish color. When exposed to the weather, the carbonates of iron and magnesia suffer decomposition, and hydrated oxydes of these metals are produced, the former penetrating the white rock, and coloring it rust or liver-brown, while the latter is separated in a dendritic form.

Ferruginous Brown Lime. A mixture of magnesian matter with carbonates of iron and manganese. When fresh, it is yellowish or reddish-white; when weathered, ferruginous. Three varieties are distinguished: scaly, granular, and compact.

Order 10. Gypsum Rocks

The rocks belonging under this head, of far less geognostical importance than the lime rocks, consist of sulphate of lime. There are two species which represent this order:

Gypsum (pl. 36, fig. 12), or the hydrous sulphate of lime, occurring as spathic, scaly, granular, compact, and breccious. The compact is most abundant; the other varieties are found in it in greater or less abundance. The characteristic color is white. Bitumen, which frequently penetrates the rock, produces a dark color, and at times beautiful markings In less quantities it colors the gypsum blue. A very pure and compact variety of gypsum is known as alabaster. Spathic gypsum not un frequently occurs in distinct crystallizations on the compact variety in a porphyritic manner. It contains various mineral substances not essential to its composition. The second variety is:

Anhydrite, or anhydrous sulphate of lime. Of its mineralogical modifications only the scaly-granular, radiated, and compact, are of geognostical importance. White prevails less, as a color, than grey and blue. Anhydrite becomes converted into gypsum by attracting moisture from the atmosphere. During this chemical action a considerable increase in volume takes place, by which whole masses are crumbled to pieces or shattered.

Heteronomic Rocks

It has already been mentioned that by heteronomic rocks we understand those in which two principal parts are to be distinguished. The one consists of hard pieces, or fragments, the other of a generally earthy, or compact mass, which cements these pieces, as it were, into a whole. To assist in furnishing a clearer view of the subject, let us illustrate the manner in which some of such species of rock may arise. In attentively examining the action of currents of water on masses of rock, we find that fragments of these are, by various agencies, broken off or loosened, and carried away. In the transportation the sharp corners and edges are worn down by the attrition produced between the different pieces, until finally the mass is reduced to an ellipsoidal or globular form. In this way may be produced boulders, pebbles, and sand. The size may vary from that of coarse sand to blocks or masses of considerable magnitude, depending upon the original size of the fragment, the hardness of the material, and the length of time during which the rolling has continued, as also upon the velocity of the current. Stones may in this way be brought from the heads of streams, and carried out into gulfs of the sea, there to be distributed in layers. The fine sand or comminuted matter suspended in the water, whether resulting from this attrition or from other causes, will be deposited when the current is weakened by its expansion into the aforesaid gulf or bay, and will occupy the interstices of these rounded stones. By the upheaving of the bottom, exposure to the atmosphere, or igneous action, the mass is indurated in the course of time, and thus a truly heteronomic rock is exhibited. This method of formation does not apply to all heteronomic rocks, many of them being produced by the destruction of isonomic rocks in other ways. An essential difference in character enables us to distinguish heteronomic rocks into conglutinates and congregates.

Conglutinates

In conglutinates the connexion of the particles or parts is effected by a combining medium of different character. This difference in character may be only in the state of aggregation, since the parts may be cemented by a mass of similar chemical character or composition. Where this is the case it is often difficult to decide whether the rock belongs to the isonomic or to the heteronomic, the passage from the one class to the other being effected by such forms.

Series 1. Sandstones.

Sandstones are conglutinates of fine grains, generally uniform in size. The part combined consists of quartz granules, which are either indefinitely angular or round. The cement is either a simple mineral or a mixture of various bodies. The principal kinds are:

Quartz Sandstone, in which quartz grains are connected by a quartzose cement. The color is generally light; grey, brownish, yellowish; seldom pure white. Its hardness is considerable.

Chalcedony Sandstone. This is of considerable hardness, as would naturally follow from its composition, consisting of quartz grains combined by chalcedony. Color grey, yellow, or blue.

Argillaceous Sandstone. This is extensively distributed, and of great importance as a building material. The cement is argillaceous, and accordingly the rock, when breathed upon, emits the characteristic odor of this substance. Its color may be either light or dark, these being sometimes so combined as to produce markings. Its hardness is less than that of the preceding varieties. The clay is occasionally separate, in masses of a spheroidal shape, as in the well-known clay stones. Mica not rarely occurs as an ingredient, and then contributes to the lamination.

Calcareous Sandstone. The cement here consists of carbonate of lime. Its colors are frequently similar to those of the preceding; it may, however, always be distinguished by the effervescence produced by acids. The cement is rarely crystalline.

Marl Sandstone. The cement is sometimes clay, sometimes lime marl. It therefore effervesces upon the application of acids, and emits an argillaceous odor when breathed upon. Colors white, green, grey, and red, these often darkened by carbonaceous particles.

Iron-clay Sandstone. The cement is an iron-clay, frequently separated in clay stones. Its principal color is reddish-brown, in which white and grey not unfrequently produce markings. It is sometimes so thinly laminated that large plates may be obtained.

Iron Sandstone. The cement is limonite or argillaceous oxyde of iron. The grain sometimes increases so much in size as to give rise to a true iron conglomerate. Colors generally dark-brown and yellow.

Series 2. Conglomerates.

The conglomerates are combinations of fragments of simple minerals or compound rocks, angular or rounded; the cement either a simple mineral or itself a conglomerate.

Iron Conglomerate. Fragments of quartz, clay slate, and, at times, of other rocks, are combined by hydrated oxyde of iron. The cement is sometimes yellow, sometimes brown iron-stone, the pieces combined being at times so sparingly distributed, that the rock passes into limonite; on the other hand, the fragments may be in such large proportion as completely to throw the cement into the background. The parts combined are often so minute as to permit the passage into iron sandstone. It is generally found in peculiar forms, particularly of tubular and stalactitic shapes. A remarkable variety is exhibited in the iron-stone conglomerate which is found in Brazil, and there termed tapanhoacanga (negro-head). It consists of pieces of specular iron, micaceous iron, and magnetic oxyde, cemented by red or brown iron-stone. Among the foreign admixtures of this rock are gold and the diamond. It is from this rock that the diamonds of Brazil and the East Indies are generally obtained.

Granite Conglomerate (regenerated granite, arcose). Crumbled, weathered granite, the feldspar of which has been entirely decomposed, is often combined in such a manner by argillaceous oxyde of iron, or hydrated oxyde, as to present an appearance not unlike real granite. The hardness of this conglomerate is less than that of granite, sometimes being exceedingly loose in its texture.

Porphyry Conglomerate. Angular or rounded pieces of more or less decomposed eurite or clay porphyry, are connected by an earthy mass, which itself appears to have proceeded from the decomposition of porphyry. The cement sometimes so completely permeates the cemented, as to render a separation impossible. With the porphyry are frequently fragments of clay and silicious slate, granite, gneiss, mica slate, &c. The general color is brown, often with light spots, resulting from decomposed feldspar. A solid cellular variety, permeated by silex, affords an excellent material for millstones.

Trap Conglomerate. Fragments of trap rocks, principally porphyritic trap and porphyroidal trap, are cemented by a mass which appears to have been produced by the attrition of the trap. This cement is often so similar to iron-clay as to be difficult of distinction. Pieces of eurite and clay porphyry, as also of granite, clay, and mica slate, are often intermingled in the conglomerate. The predominant color is reddish-brown with a violet tinge.

Iron-clay Conglomerate. Fragments, partly angular, partly rounded, of the most different simple or compound rocks, are combined by an iron-clay of an earthy weak fracture. The cemented parts are principally pieces of quartz, feldspar, clay and silicious slate, granite, gneiss, flagstone, and various porphyries. Their size varies from the largest lumps to the grain of the finest sandstone.

Grauwacke. This is a conglomerate which undergoes the widest modifications. Lumps and fragments of the most various kinds are combined by a clay slate cement. There generally occur in it quartz, silicious slate, clay slate, feldspar, mica, granite, various porphyries, and other compound rocks. Quartz seems, however, to predominate. The fragments sometimes occur in such proportion as completely to hide the cement. Grauwacke varies greatly with respect to the grain: while, on the one hand, the rock is composed of no inconsiderable pebbles or rolled fragments, on the other, these are so imbedded in the cement as to lie entirely concealed. The cement even appears at times to be coarser than the parts cemented. A grey color predominates. The three varieties which have been distinguished possess an essentially different character as regards their structure. Common grauwacke is the modification exhibiting the components most clearly. To this belong the coarse, small, and fine-grained grauwacke, all of considerable solidity. The slaty is a finely granular variety, generally of a thick lamination. On the surface of lamination, clay-slate and mica not unfrequently, occur conformable to the lamination. We must not confound this with grauwacke slate, which appears exceedingly like clay slate, and sometimes passes into it. The mixture is very thorough, and the lamination less evident than that of clay slate. Besides the difference in fracture, the two rocks may be distinguished by their mode of cleavage. While clay slate may be separated into acutely-angled parallelopipedal pieces, the cleavage of grauwacke slate is into ellipso-spheroidal concentric shells.

Silicious Conglomerate. Rounded or angular pieces of silicious mineral are cemented by a silicious medium. Its hardness and solidity are considerable; the predominant colors grey and white. The grain is very various. It may be so fine as to pass into sandstone. Pudding-stone is a silicious conglomerate in which rounded fragments of flint are cemented by silicious matter.

Nagel-fluh (calcareous breccia). This peculiar name comes from the Swiss, and means nail rock. The appellation has been derived from a peculiar appearance presented by the weathered rock, in that the pieces of cemented matter protrude from the surface, like so many heads of nails or spikes. The portions cemented are united by a medium of similar character, only of a finer grain. This rock is distinguished into silicious, calcareous, and common breccia (nagel-fluh), as either of these ingredients is in excess, or neither predominates. The size of the particles varies considerably, as does that of the grains of the cement.

Calcareous Conglomerate. Blocks or fragments of various rocks, as lime, clay, silicious slate, &c, are united by a calcareous cement, often penetrated by oxyde of iron. Pieces of lime predominate. The compact or earthy cement is sometimes crystalline.

Shell Conglomerate. A combination of shells, generally broken, or corals mixed with quartz or other silicious minerals, united by oxyde of iron, limestone, or calcareous sinter. The rock is sometimes soft, sometimes hard and compact; in the latter case it affords an excellent building material.

Trachytic Conglomerate. Fragments, generally angular, of trachyte or its allied rocks, as pearl, pitch, pumice-stone, and obsidian, are connected by a cement resulting from the chemical decomposition and mechanical attrition of these same substances. The fragments vary from a diameter of several feet to the size of a nut, the latter being most prevalent. This rock, on the whole, possesses little solidity; it often contains opal in its various modifications. The varieties are:

Trachytic Breccia, or trachytic conglomerate, with the contained fragments, generally angular, and predominating.

Trachytic Tufa. The opposite here prevails, the cement predominating. Here belong some rocks which are distinguished by their color and structure, but are only modifications of trachytic tula. Thus we have peperino, which presents an ash-grey cement, whose uniformity is interrupted by slaggy particles and glassy feldspar; also the pausilippo-tufa, of a yellow color, and frequently possessing a certain porosity; together with the Rhenish tufa, tras or terras, in which pieces of pumice are joined together by a grey earthy mass.

Basalt Conglomerate (trap tufa, Tuff-wacke). This rock is a conglutinate of basaltic fragments and of various other rocks, which are combined by an attrition-product of the basalt. Vesicular basalt is of most general occurrence, as also clinkstone trachyte, granite, sandstone, mica slate, and quartz. Augite, basaltic-hornblende, olivine, wood-opal, brown coal, and some other mineral substances, are often distributed throughout the earthy mass. The hardness is inconsiderable.

Leucitophyre Conglomerate. The character of this rock is much like that of the preceding. Fragments of leucitophyre, or of similar rocks, are combined by pulverized leucitophyre substances. Leucite frequently occurs in perfect crystals, as also mica and augite; more rarely melanite and hauyne.

Pumice Conglomerate. This is composed of pumiceous matter cemented by a clayey substance. It is generally very light and porous, but, with some degree of hardness, furnishes a good building stone.

Congregates

These are combinations of different particles which possess so little coherence as to form soft, light, or loose aggregates. Congregates are heteronomic masses in which the cement is wanting.

Series 1. Clays.

The clay of the mineralogist occurs also in masses entitling it to the attention of the geologist. It is a silicate of alumfna, with a varying proportion of water, contaminated by a number of different substances whenever it occurs in large quantity. Among these substances are especially to be found lime, coaly and bituminous particles, oxyde of iron and sand, which may be separated by washing. A preponderance of any particular ingredient determines its character, as:

Iron Clay, which contains a considerable proportion of oxyde of iron, and is therefore of a reddish-brown color.

Marl Clay, containing a large amount of carbonate of lime, and exhibiting various modifications, as the ferruginous, common, sandy, and bituminous.

Drawing-Slate. This is a clay slate penetrated by a considerable quantity of carbonaceous matter. It produces a streak, and is brought into trade under the name of black chalk. It is of a pure black color.

Bituminous Shale, or burning shale. This is a clay shale, impregnated by bituminous matter. It is distinguished from drawing-slate by its power of burning with a flame. The color is rather brown than black.

Clay Shale, an earthy clay of more or less slaty structure, and of a grey color, running into black by the addition of carbonaceous matter. It has a powerful attraction for water; so much so, that when the tongue is touched by a small piece the two adhere firmly.

Clay. Of an earthy consistence, and readily rendered plastic by water. It contains sand more or less easily removable by washing. Several kinds are distinguished:

Porcelain Clay. Of a white color, which is permanent in baking. It is closely allied to kaolin, or clay resulting from the decomposition of feldspar.

Pipe Clay. Of a grey color, produced by a slight admixture of bituminous matter. This clay becomes white by burning, and is well adapted to the manufacture of tobacco pipes and common ware.

Potters’ Clay. Of various colors, grey, yellow, and reddish-brown.

Loam. This occupies a place intermediate between clay and sand; it is of an earthy and sandy feel. The sand, distributed in great quantity, although not always visible, may readily be felt. Colors grey, brownish, and reddish. When it contains much lime it becomes marl loam.

Series 2. Soils.

This series embraces thorough and loose mixtures of various substances. The conditions of aggregation, as well as the colors, are exceedingly diversified, these being modified principally by a greater or less proportion of humose substance, and by iron, and perhaps manganese combinations. The different soils vary much in their capacity of taking up water. The weathering of various rocks, as well as their mechanical separation or division, is the principal source from which they are derived; for this reason their composition is of great diversity. Lime, magnesia, potassa, soda, and oxydes of iron and manganese, are of most general occurrence as bases, these being combined with carbonic, silicic, sulphuric, phosphoric, and nitric acids, as also with chloric and fluoric. The organic matters consist of vegetable mould under various forms, as humus, geine, ulmine, humic and ulmic acids. Salts of ammonia also occur. Particular kinds are determined by the predominance of individual ingredients; the full investigation of these soils and their properties belongs not to this subject but to agriculture. The principal of these soils are:

Clayey Earth. An earthy mass with clay in excess. It absorbs a large quantity of water, thereby becoming plastic; on drying again it becomes very hard, and exhibits extensive cracks and fissures, owing to the shrinking in volume. The consistence of the soil is generally solid. Grey, yellow, brownish, and bluish, are the most conspicuous colors.

Loamy Soil. This occupies a position intermediate between a clayey and a sandy soil, just as loam does between clay and sand. The earthy mass is generally of a brownish or yellowish-grey color, furnishing a fruitful land when calcareous particles enter also into combination.

Sandy Soil. This contains an excess of quartzose sand, in an earthy, clayey, or marly mass. It is very loose, and of a grey, yellowish, or whitish color, takes up little water, parts with it readily, and quickly becomes dry.

Calcareous Soil. An excess of calcareous particles in loose mixture with clayey and sandy matters. It is of a light color, often changed by humose substances. It absorbs water, yet without becoming plastic, and readily parts with it again. It overlies chalk, calcareous tufa, and other limestone rocks.

Iron-clay Soil. This is of a reddish-brown color, and arises from disintegrated iron-clay or decomposed ferruginous rocks. It readily takes up water, and holds it von tenaciously. On the escape of the water the earth shrinks and becomes fissured.

Iron Soil. This is of very complex composition, and appears to be principally a product of decomposition of pyroxene and amphibolic rocks. The considerable proportion of oxyde of iron imparts to it a yellowish or brown color, ll absorbs much water, retains it firmly, and parts with it again without fissuring.

Humose Soils. The humus which characterizes this soil rarely amounts to over one fourth of the entire mass. Sand, clay, and more rarely lime are associates in it. When dry it is very apt to be dusty, and when wet of a boggy or miry character: its color is brown or brownish-black, It readily combines with water, and contracts slightly on drying. Many kinds ot" humose soil are known in agriculture, A.mong these the heath soils are conspicuous: soils with remarkable hard particles, resulting from the decomposition of species of erica or heath.

It frequently happens that fragments and blocks of various rocks are distributed in soils, of various shapes and sizes, and in such excess as almost to displace the soil itself. The manner and origin of their accumulation, as well as the petrographical peculiarity of these fragments, are entirely dependent on the position of the bed of the earth. The most conspicuous ingredients occurring here and there in soils are gold, arsenical pyrites, and iron pyrites. The ground is frequently impregnated with various salts, which, under favorable circumstances, effloresce so as to form a white incrustation. The principal of these salts are common salt, glauber salts, epsom salts, potash and soda, saltpetre, &c.

Series 3. Sands.

These embrace masses presenting themselves as accumulations of fine angular or rounded grains. They are generally quartzose, although other substances than quartz max constitute sand. The principal species are:

Quartz Sand, or a loose accumulation of quartzose particles. There are various modifications, characterized by a greater or less degree of purity. Yellow sand derives its color from hvdrated oxyde of iron, this being so firmly combined as to require the action of acids to eradicate it. The principal varieties of sand are characterized by the presence of lime, dolomite, augite, garnet, iron, mica, gold, platinum, shells, &c. Jewel sand contains many o\ the precious stones, as diamond, spinelle, zircon, garnet, &c.

Series 4. The Gravels.

Here belong those very loose aggregates which plainly exhibit traces of a long-continued disturbance of various rocks. One of the furnish the whole supply, or several may be combined. They are known as granitic, porphyritic, syenitic, marly, tufaceous, calcareous, basalatic, pumiceous, &., gravels.

Series 5. Pebble Beds.

These are distinguished from the last by the rounded character of the rid by their generally smaller size; the principal kinds are the calcareous, silicious, and gem beds. Fragments of sapphire, topaz, chrysoberyl, of gold and rare ores, are often found associated.

General Oreography

The rocks, whose consideration, according to the system of Hausmann, we have just completed, are those which, in greater or less accumulation, compose the crust of the earth. Great diversities, however, are exhibited in the manner of their occurrence, as well as in the relations they bear to each other. The surface of the earth appears to present to us the greatest diversity of structure, in the most varied, and apparently inequalities of elevation and depression; precipitous declivities washed by rushing waters, rise up in fruitful valleys, and mountain ranges bound to the horizon in the blue distance. Here are displayed smiling fields, or meadows embraced by nobile forests cover the extended plains; there is seen a sandy waste, seemingly capable of supporting only the sparsest vegetation, while in another place, jagged rocks stand out from cloud-capped heights, shutting out the beams of the setting sun. Seas, with foaming waves, wash away the costs and reveal the buried secrets of the earth. These irregularities and inequalities are, however, by no means accidental; they proclaim great causes, which have thus modified the surface of the earth. Since stones or rocks compose the crust of the earth, and cause these irregularities, a new field opens to us in the investigation of rock formations (oreography). This department of our subject treats of rocks as they occur in great masses. Investigations of this kind have lead to the most astonishing and stupendous results, in revealing to us the certain or probable action of mighty causes, in producing the effects we see around us. The solid crust of the earth is well calculated to exhibit the traces of expended forces; not so with the atmosphere and the terrestrial water. The hurricane may rage, and the waves be one moment heaped up mountain high, and the next sink down again into the abyss; lightnings may play and thunder roll; yet the waters when calm and the sky when clear, exhibit not a vestige of the commotions which agitated them; Not so with regard to the coast, whose incumbent rocks have been shattered by the surge, or the forest, whose vegetation has been mowed down by the blast; they (and the solid portion of the earth’s crust) along present durable evidence of such mighty agencies. If again, we examine the phenomena caused by volcanoes, where torrents of lava have annihilated blooming fields, where subterranean explosions have shattered mountains, where showers of ashes have buried cities, and earthquakes have paralysed whole nations with terror, there it is that nature cannot so readily erase the traces of such catastrophes. In such ways changes of original condition may occur, leaving a very definite character. These changes are to us the hieroglyphics which describe the past history of our planet, and the unriddling of which is the business of the geologist. He indicates the causes, the geognosist only the effects. Causes, however, are known by their effects, and for this reason the study of the latter must precede that of the former. As in the investigation of any object the exterior must first be subjected to examination, before the internal peculiarities can be studied, so we but act according to sound reason in going first into the consideration of the exterior of mountain masses, and then into that of their interior, the structure, and the constituents. This spheroid on which we live, and whose polar flattening amounts to \(\frac{1}{300}\), possesses an average density of 5.67; or in other words, its density is 5.67 times that of pure water. The mean density of the earth’s crust is, however, but 3.0; it must consequently increase towards the centre, and become greater than 5.67. If we assume that part of the earth whose density is 3.0, to extend to a depth of one fourth its radius, then the density of the interior must exceed that of wrought iron, or be more than 7.7.

It has been calculated that nearly three fourths of the surface of our planet are embraced by the sea level. All above this level is called land, all below it sea. The rise of the land above this level is found to increase with the distance from the sea, forming the general elevation, the ever descending bottom of the sea constituting the general depression. These general elevations and depressions bear the same relation to our whole planet that special elevations and depressions do to limited tracts. It is the alternation of mountain and valley which modifies the continent, as also the bottom of the sea. Pl. 53, fig. 9, is a submarine section of the Straits of Gibraltar, fig. 10 a section taken between Tarifa and Alcazar on the Spanish coast.

Mountains

The height of mountains, as well as the depth of valleys, varies to an extraordinary degree. It is man, not nature, who limits the almost imperceptible transition from the low plain to the highest mountain, by his artificial definitions. As, however, it is necessary to have some standard of comparison, it is customary to call an elevation of 100 feet or less, a hill; one under 3000 feet, a low mountain; one under 6000 feet, a mountain of medium height. Anything beyond this last limit is known as a high mountain. In measuring the heights of mountains it becomes necessary to determine the length of a line supposed to be let fall from the summit to the extended level of the sea. This line evidently expresses the relative heights of mountains, or their respective heights above the level of the sea. The relative height must be distinguished from the absolute, or that of a mountain from its summit to its base. For measuring heights of mountains the theodolite is the most appropriate instrument, being capable of a very accurate determination of angles. If a station be selected from which the summit of the mountain in question can be observed, and the angle measured which the line of direction to the summit makes with the horizontal, and the horizontal line be measured towards the foot of the mountain, and the angular elevation of the top again taken from the other extremity, then we shall have all. the data necessary to a trigonometrical determination of the point in question. The more usual instrument for measuring heights is, however, the barometer, the mercury in which stands at a different elevation with every difference in the distance from the level of the sea. The apparent simplicity of this method is nevertheless affected by several modifying causes, as the amount of moisture in the air, the temperature, the character of aerial currents, &c.

Every mountain may be divided into the top, summit, or head; the middle, face, or body; and the bottom or foot. The plane on which the foot is supposed to stand is called its base, and the faces of the mountain are formed by the declivity or slope.

The mutual relations in which the single parts of the mountain stand to each other determine its form, and of this we distinguish two principal types. Mountains proper are those whose length and breadth are pretty nearly the same, mountain ridges those whose length considerably exceeds the breadth. True mountains exhibit considerable diversities in theit external forms; sometimes they resemble a segment of a sphere or paraboloid, sometimes a bell, a cone, or a pyramid. These various forms are not so uninteresting as might at first be supposed; the external appearance in itself may not, indeed, indicate any fact for geognostical consideration, it may, however, illustrate the peculiar relations existing between external form and the kind of rock. The generalization has beer made, that the same rock species, when in not too inconsiderable quantity has constant external features, so that a practised eye may, in many cases draw an accurate inference as to the character of a mountain from a far distant view of it. Thus granite generally assumes the form of a spherical segment, trachyte that of the bell, while volcanic masses occur in the shape of a cone. The differences which exist amongst mountain ridges may have reference either to the ridge itself, or to the vertical cross-section. In the first point of view we distinguish between straight and curved ridges; in the second, between a circular, a parabolic, and a roof-shaped cross-section. In considering the slope of a mountain the geognosist first investigates the angle which it forms with the horizon. This angle, capable of infinite variation, is exceedingly difficult to ascertain, even approximately, without instruments, its determination being very much exposed to optical illusions. It becomes necessary to set artificial boundaries between the most frequent angular differences, and to express them by artificial appellations.

There may be modifications in respect to the continuity of the declivity, which contribute in great measure to the character of the mountain. This may either be uniform and uninterrupted, or may have a stairway or terrace form: it may be cut up by furrows or intersected by ravines. The foot of the mountain, which in its slope and expansion may exhibit considerable diversity, experiences on the whole the same variations in the angle of inclination as the descent; this angle is, however, different from that of the body. The summit or top also varies much in shape in different instances; it is either acute, sharp, jagged, hunch-backed, rounded, flat, hollowed, or saddle-shaped. It is the manifold combinations of the different shapes of head, sides, and foot, that give such diversity to the appearance of mountains, and render it possible that, mountainous regions may appear different in different places; each individual mountain may thus excite a fresh interest in the mind of the observer.

Combinations of Mountains into Mountainous Regions and Ranges

It is very seldom that mountains occur entirely isolated; it is only single volcanic cones that are elevated abruptly from the midst of a plain. In by far the greater number of instances they are united into groups, and brought together in the most varied manner. In most cases mountains are arranged into what we call mountain chains. The mountain chains may extend in one or several directions; they may vary in length, breadth, height, and connexion. We can generally detect characteristics in the mountains which permit a distinction into two principal sections. They exhibit, with respect to the collocations of the mountains, either a certain want of system, or an arrangement according to definite laws. The first appearance is presented in very many hills or mountainous regions, as, for instance, in the extinct volcanic district of Auvergne (pl. 45, fig. 2), while the latter, which is of much higher interest, is a peculiarity of the mountain range proper. Most generally mountains occur, one after the other, so as to form a mountain range of greater longitudinal extent than lateral. This is the mountain chain as distinguished from the mountain group, which is of tolerably equal dimensions. The Hartz Mountains afford an illustration of the combination of both forms. Mountain chains are more frequently met with than mountain groups; this, however, does not appear to be the case on all the planetary bodies, as we may readily convince ourselves by an examination of the moon through a telescope. The immense number of volcanoes, with vast craters, in which again cones of eruption arise, are not to be mistaken in these mountain groups. In a mountain range there is always one part which can be distinguished as possessing the highest level; this is called the principal ridge, its highest portion being called the comb or crest.

Mountain ranges, like single mountains, exhibit a slope equal to the mean value of the angle of inclination for the individual mountains. In comparing the parts of a system of mountains with those of a single mountain, we shall soon find that a parallel cannot be drawn throughout, but that in the former there are parts which do not similarly occur in the latter. Examples of these are to be seen in such systems as Monte Rosa, where the mountains are grouped concentrically, as also the mountain heights, single portions shooting up here and there independent of the rest; plateaux or planes, often inclosed by the highest mountain peaks, and at a great elevation above the level of the sea, passes, elevated extents of land lying between mountains connecting opposite slopes, and thus producing a saddle form. A pass of this kind occurs on the St. Gothard, lying 6390 feet above the level of the sea, and bordered on both sides by mountains over 9000 feet in height. Here belong also the plains found on slopes of the mountains, as also the spurs which separate and run out from the body of the system.

Mountain crests are very generally (especially in mountain chains) ranged one after the other, thus giving rise to a narrow linear extension, called a mountain range. Such ranges occur in greater or less number in the same mountain system; they generally run out from one, more rarely from two or more primary ranges, these latter being then parallel to each other. In mountain chains the primary range is called the longitudinal, from which run out the lateral or terraced range or spur. We must also distinguish secondary ranges from the tertiary ranges. The ranges in mountain groups have generally a radiated direction. The height of the secondary ranges usually decreases with the distance from the primary range; this, however, is not always the case.

The connexion of mountain systems, when such exist, may be effected either immediately or indirectly. Mountainous or hilly land is generally the link which effects the union; it is thus between the Hartz and the Thuringerwald, between the Alps and the Chain of Jura. Where the outposts of one mountain system extend their arms into the valleys of another, the alliance is immediate; this is the relation between the Alps and the Appenines. Just as the forms of mounts and mountains are exceedingly various, so is it in respect to their external features. Plane surfaces alternate with those that are hilly, rough, and full of cavities; steep rocks with deep fissures.

Valleys

As valleys are produced by mountains, it is natural that the peculiarities of the former should depend on those of the latter. At first glance into a valley two features are readily recognised: one of these the bottom, and the other the walls or sides, produced by the inclosing mountains. If we suppose a valley to be intersected by a plane at right angles to its axis, many diversities will be observed in this cross-section. The bottom of the valley is either straight or curved, occurring both convex and concave. In respect to longitudinal extension, valleys are either horizontal or inclined at various angles. An interesting phenomenon is presented by the successive descents in valleys, seen particularly in the transverse valleys (those which intersect the longitudinal valley of a mountain chain nearly at right angles). The occurrence of many waterfalls is intimately connected with this feature in valleys. Valleys are sometimes completely inclosed by mountains, in which case they are generally circular or elliptical in shape, and are often converted into lakes, as is the case with Derwentwater, or the Lake of Keswick (pl. 51, fig. 2), in the county of Cumberland, England. Valleys which are half inclosed, generally extend far in a longitudinal direction, and have but one outlet, while the open have this on two sides. The latter, the open, are also called valleys of interruption, as they generally connect two longitudinal valleys, and therefore break through, as it were, the separating ridge.

The study of the relations in which the valleys of a mountain system stand to each other, is of extraordinary interest, this being increased in many cases in proportion as their character enables us to recognise a certain causal connexion. This, however, can only be elucidated after a close comparison of the relations of stratification has been instituted; we shall therefore first consider the relations in which valleys stand to mountains and to mountain ranges. Those valleys which lie within the limits of a system of mountains are called mountain valleys, in distinction from outer valleys lying to the outside of the same systems; both, again, differ from intermediate valleys which separate two contiguous systems. Since valleys are bounded by mountain ranges or spurs, and as we distinguish three kinds of these, it naturally follows that the valleys will also differ among themselves. Accordingly we separate primary or longitudinal valleys from lateral or cross valleys, as well as from secondary valleys, these being all bounded by the corresponding mountain ranges. Longitudinal valleys have generally a considerable extension in length, and but little in breadth, the surface presenting much uniformity of appearance. The case is precisely the reverse with the cross and secondary valleys; these, on the whole, are shorter, and alternately expand and contract, often run out into ravines, their walls being not unfrequently formed by remarkable rocks. We also find here the peculiar terrace-like character, with the accompanying waterfalls. In mountain chains the corresponding valleys exhibit a more or less parallel arrangement; in mountain groups they exhibit a radiation more or less complete. A phenomenon of no very rare occurrence is the mutual intersection of valleys at different angles.

Plains

When valleys are very broad they pass into plains, no well denned limit between the two being possible. The character of plains may experience modifications by taking their boundaries into consideration. Under this point of view we distinguish coast and interior plains. The former are such as are bounded on one or more sides by the sea, the latter being inclosed on all sides by mountains or mountainous land. These, however, are rather geographical distinctions; to the geologist the division into depressed plains, plains proper, and elevated plains (plateaux), is of much more importance. The first lie below the level of the sea, the second are elevated slightly above it (as the coast of Holland), and the third, sometimes called tablelands, are at a considerable height above the sea, as in the plateaux of Bavaria and Mexico. The same difference exists between the level of inland waters and that of the sea. Thus the surface of the Caspian Sea is about 31ft. below that of the ocean, and that of the Dead Sea about 1300ft. The bed of the Jordan, in part, lies below the level of the Mediterranean. This is unquestionably the case with the sea of Tiberias. Pl. 45, fig. 3, exhibits a section of Judaea through the basin of the Dead Sea, from which these relations may be readily seen. In general, however, inland bodies of water are higher than the ocean, at times very much higher, as instanced by Lake Titicaca in Peru, existing at an elevation of 12,800ft. (pl. 45, fig. 12). The size of the lake or sea generally decreases with the elevation.

The Interior of Mountains

We turn now to a brief consideration of the interior of mountains, after having thus examined the peculiarities of their external form. The simple fracture of a stone, of a naked rock, and especially mining operations, soon show us that the interior does not consist of a simple homogeneous mass; on the contrary, we perceive that various rocks alternate with each other, and are split up into smaller parts of a great mass. We see cracks crossing through one another, and often in such a manner as to form subdivisions of definite form. These portions often exhibit a certain goniometrical character, comparable with crystallization, which comparison, however strictly speaking, is not allowable. If we consider the real character of a crystal, we shall soon find that no analogy exists between it and such a separating fragment, further than that of general external form, the edges, corners, and faces, not obeying strict crystallographical laws. The relative positions borne by these masses of separation or cleavage to each other are known as structure.

Cleavage of Rocks

Masses of cleavages present themselves under two points of view, as angular and rounded. The latter are produced when the planes of cleavage return into themselves, these shelling off on further cleavage. Whether the cleavages be straight or curved, if they occur in one plane, this is called the plane of cleavage, which may extend over small spaces or through entire masses. The cleavage of rocks occurs in various degrees of completeness. The application of force is sometimes necessary to separate the cleavage masses, others are entirely separated, and in other cases, again, the spaces of separation are no inconsiderable cavities. In dealing with cleavage it is necessary to ascertain whether such be essential or non-essential; whether it stand in prime connexion with the character of the interior or not. The non-essential are entirely accidental, and are called joints. In the actual structure of rocks we must necessarily distinguish true cleavage from stratification.

True cleavage never extends to so great distances as stratification. The parts into which cleavage planes divide rocks are referable to a rounded and an angular form. Of the former class we have the sphere, the spheroid, the ellipsoid, the elliptic spheroid, and the indeterminate surface. These forms frequently exhibit a concentric cleavage, as seen in basalt, granite, porphyry, &c. (pl. 43, fig. 23). Most frequently, however, the cleavage is plane.

The angular forms are either indefinite, columnar, or parallelopipedal (prismatic). The first class comes nearest to the spherical form. Thus lumps of menilite are found in adhesive slate (Jameson) coming very near to an aggregation of spherical segments (pl. 43, fig. 22). The columnar form is most frequently seen in rocks which have passed from a melted liquid condition into the solid. Basalt is especially adapted for the study of columnar structures. The six-sided prism must be assumed as the primary form from which the three, four, five, seven, &c., have been derived as irregular or imperfect developments. In basalt a sphere is not unfrequently combined with the column, easily recognised in the alternate bending in and out of any two edges of the column, and their accompanying thinning and thickening. A single column is generally divided into numerous joints by transverse cleavage (pl. 53, fig. 11), the spherically convex end of one joint fitting in the spherically concave end of the next (pl. 53, fig. 13). When the spherical segment is somewhat greater it forms projecting sharp corners to the edges of the prisms, a feature not unfrequently seen in the basaltic pillars in the Island of Staffa. Entire mountain masses sometimes exhibit this structure, which is especially peculiar to lava currents, as shown in pl. 43, fig. 24. The columns often consist of small plates inclined irregularly to the principal axis at different angles (fig. 25). Porphyritic columns occur in this manner on the Wachenberg near Weinheim. A peculiar phenomenon is sometimes exhibited when a melted mass, subjected to great pressure, has been forced up so as to fill a crack or fissure in the rocks. On cooling, the columnar cleavage arises, and the extremities of the columns stand at right angles to the sides of the fissure. Thus, if the fissure be vertical, the columns will be horizontal, and vice versa. Pl. 43, fig. 16, is intended to elucidate this phenomenon. In the vertical fissure, b, the columns are horizontal, while the horizontal masses below c and d have vertical columns. In large masses this rule does not seem to hold good, the columns being combined like billets of wood in a charcoal pit, or else lie grouped irregularly, one upon another. This is shown very clearly in the Island of Staffa (pl. 49, fig. 7).

As the columnar form is peculiar to rocks of igneous origin, so the parallelopipedal is restricted almost exclusively to those which have been deposited from water. Both the rectangular and oblique parallelopipedons occur; the former of cubic, pillar, square, and tabular forms.

Stratification

Stratification, which always extends over greater distances than true cleavage, is peculiar to rocks deposited from water. Plutonic rocks are sometimes subdivided in a manner bearing a great resemblance to stratification; the affinity in structure is, however, only apparent, not real, the subdivisions being merely a tabular cleavage of columns or parallelopipedons. Granite often presents this appearance, as shown in pl. 43, fig. 12, where the corners and edges of the separated portions have been rounded off and weathered away by atmospheric agencies. Stratification and cleavage may occur together, as is often seen in slate rocks, whose cleavage planes, parallel constantly to each other, intersect the planes of stratification at all angles.

The portion of rock included between two planes of stratified separation is called a stratum. The thickness of strata is exceedingly variable, and not unfrequently immense beds are found to alternate with quite thin layers.

The planes of stratification are generally straight, although not always of great extent. At times their general direction is straight, with occasional undulations, curvings, and contortions (pl. 43, fig. 8). These bendings and foldings, which sometimes give rise to the formation of caves (as in the grotto of Jupiter on the Island of Naxos, pl. 51, fig. 8), often run into the finest crumpling, as may frequently be observed in clay slate, this rock being, for other reasons, especially adapted to the study of stratification, Silicious slate is not unimportant in this respect, a complicated stratification being peculiar to it. The strata are often entirely curved (pl. 53, fig. 8, representing clay slate strata on the coast of Scotland, and pl. 43, fig. 9, strata on the coast near Wapness, not far from Guns-Greern), this condition being more interesting than a partial flexure. There are two principal differences in this respect, according as the opening of the bend is above (pl. 43, fig. 5) or below (fig. 7); as also, whether the bend be arched or angular like the roof of a house. When the opening is turned up we have a trough: when below, a saddle. Troughs and saddles generally succeed each other, as seen in great perfection in a section of Brittany, between Rennes and Nantes (pl. 46, fig. 3).

Strata frequently exhibit a change in their position, so that one part of the same layer stands at a higher or lower level than another. When the variation is inconsiderable it is called dislocation; where of greater amount, displacement. These frequently stand in such connexion with veins and fissures as to render it not unreasonable to ascribe all to the same system of forms.

Arrangement of Strata

The position of planes of stratification is either horizontal, vertical, or inclined at various intermediate angles. The horizontal position is of least interest, what little it possesses arising from its relation to the inclined. In inclined strata the geognosist has first to deal with dip or inclination and strike. The dip of a stratum is the angle which it makes with a horizontal plane, and the strike the angle made by a horizontal line of the stratum with the meridian. The direction has also to be considered in the dip. For determinations of dip and strike, the mining compass, with a pendulum and graduated arc attached, is the most convenient instrument.

The planes of stratification are either parallel or convergent to a greater or less degree. When the latter is the case a fan-shaped stratification is presented, in which the planes of stratification all appear to converge towards one point, diverging from one another in the opposite direction.

Relation of Stratification to Mountain Masses

The relation of stratification to mountain masses is of great importance, their whole character depending on it. Mountains and valleys are arranged similarly with their predominant strata. It has already been mentioned that stratification is peculiar to rocks which have been deposited from water; it will therefore be readily understood that the general arrangement of strata must be horizontal, or not very far from this position. That all strata, however inclined, contorted, broken, or disturbed, were really once horizontal, is a proposition which admits of no doubt, with the powerful reasons in its favor furnished by geological science. The question immediately presents itself, however, by what means have the strata been elevated? What kind of force has produced such effects? The answer to these queries we find in the investigation of those rocks already ascertained to be of igneous origin. The peculiar manner in which these latter occur, the relation in which they stand to the stratified masses, and the alterations they effect in the petrographical condition of the same, fairly authorize us to look upon such igneous masses as closely connected with the phenomena in question. Thus, on the coast of Dorsetshire we shall find beds of chalk upheaved by basalt (pl. 52, fig. 8). An upheaval of rocks of the Jura (pl. 43, fig. 13, b, c, d) by abnormal masses is seen near Freiberg in Breisnau, and in the canton Bern (fig. 14). This will be referred to more fully hereafter; at present our main object is to consider the relation of strata to mountain masses. To do this properly it would, perhaps, be convenient to name valleys according to their origin. The difficulty here, however, would be in the introduction of theoretical views into nomenclature, which might be embarrassing to a beginner in science. Thus, longitudinal valleys might be called valleys of elevation, their formation being contemporaneous with the elevation of the mountains. A longitudinal valley is generally so constituted that its strata are parallel to the slope of the mountain which has given rise to it; thus, if we suppose horizontal strata to be elevated by two forces acting parallel to each other, the valley will lie between the two mountain ridges thus produced. Single circular valleys must also lie included among the valleys of elevation, where the strata lie around parallel to the mountain slope. An excellent illustration is found in the valley of Pyrmont (pl. 44, fig. 1), where the elevating mass lies under the strata, as of the variegated sandstone, without having broken through. Upon this lie the strata of the muschelkalk, b, and upon this, those of the keuper, c. The strata b, as well as c, occur on both sides, and were formerly continuous, having been separated at a subsequent period. When the strata were too brittle to admit of a considerable bending, they have been broken. Thus, while in this fissure a steep descent on both sides, along the axis of elevation, must exist, on the other sides, in a direction transverse to this axis, the slope will be more or less gentle. These relations, of no unfrequent occurrence, are shown sectionally in figs. 2, 3, 4, and 5. In fig. 2, the elevating nucleus has broken through, the strata resting on it on each side. The steep declivities of the faces of the strata are turned towards the head of the nucleus, the planes of stratification lying parallel to the slope. In fig. 3, the mass of elevation constitutes only the base of the valley, as also in fig. 4, where the strata are of unequal thickness. Should an elevation of the latter kind take place under water, as seen in fig. 5, so that the strata project only on one side, the mountain chain appears to consist of one such lip, the other being concealed by the water. The strata may often slope so much along the nucleus, as that this shall occupy the higher level, as on the Brocken in the Hartz (pl. 43, fig. 15), where the ganite, a, lies higher than the strata, b, c, d, e, f, of the transition-slate formation. If the non-conformable mass be in great preponderance, the conformable may be torn entirely asunder. Valleys thus produced are called valleys of disruption (pl. 45, fig. 1).

Before we proceed further in this part of our subject, it may be advisable to mention a few of the technical terms employed in the consideration of stratification. The terms dip and strike have already been referred to. If we conceive a longitudinal force to act in upheaving a succession of strata, the line or plane in which the disturbed strata would meet if produced, is called the anticlinal axis or line. In other words, it is the line in a chain of hills or a valley from which the strata dip in two different directions. The synclinal line or axis is that along which opposite strata dip towards each other. When strata are parallel to each other, whatever be their dip, they are said to be conformable. When strata rest on the edges or faces of other strata, in such a manner as to render it evident that all are not of contemporaneous origin nor have been exposed to a simultaneous force, they are called non-conformable. An out-crop of strata exists when the edges of these strata have been elevated by the disturbing force so as to come to the surface. When strata have been broken or dislocated by some force, so that the continuity of the individual beds is interrupted by the sinking down or displacement of one of the portions, a fault is produced. When the fissure or split is filled up by injected igneous matter, a narrow wall is exhibited, called a dyke.

Valleys sometimes occur as excavations produced by the abrading action of currents of water. This fact can be readily ascertained from an examination of the stratification on opposite sides; this existing in the same plane on both sides of the valley (pl. 43, figs. 1 and 2). Such are called valleys of excavation or denudation. In pl. 43, fig. 3, the same stratum, a, is seen on the left-hand side much higher above the bottom of the valley, B, than on the right side, without any difference existing in the general direction. The determination of the true character of mountains and valleys from the nature of the accompanying stratification, however simple it may be theoretically, is yet very much embarrassed in practice, by the vegetation and surface soil which hide the subjacent rocks. In individual cases, however, this difficulty does not exist, and the whole problem can be solved at a single glance. These relations are beautifully seen in parts of the Mont Blanc chain, whose tabularly cleft rocks are presented with vertical fissures. Weathering causes the loss of considerable portions, as is often the case with granite and gneiss. In this way steep pyramidal rock walls are left, which form the boldest and most singular groups. Some idea of this condition of things may be obtained from an examination of pl. 44, fig. 10, this representing a view of the Mont Blanc chain from the Breverberg. Here a indicates the celebrated vale of Chamouny; b, Mont Blanc; c, La Mer de Glace, a glacier; d, the Bosson’s glacier; e, l’Aiguille verte; f, le Dome du Goute; g, la Montanvert. This character of rock surface exhibits a magnificent appearance when traversing whole ranges. The names of horns, needles, teeth, &c, given to the different projections by the inhabitants of the Alps, are derived from real or fancied resemblances. The vicinity of Barschwyl in the Solothurn Jura, shows beautifully the manner in which the character of stratification influences the external form of a country. The strata are entirely denuded, and their relations to the mountain formations is evident at a glance (pl. 44, fig. 11). Mountain forms become remarkably modified when rocks of different petrographical character alternate with each other. Harder and more durable strata, a (pl. 44, fig. 12), alternate with others of much softer texture, or readier destructibility, b. The former remain standing in extended rock walls, while the latter disappear to a greater or less extent. Terraced valley slopes may be produced in the same manner (pl. 44, figs. 13 and 14).

Accidental Separation of Rocks

The parts produced by accidental separation of a rock mass, or by fissures and joints, possess an undefined, irregular form. They are entirely incidental in their origin, and may either be confined to a small space, or traverse whole mountain masses. The fissures are of various sizes, from thin cracks to extended and sometimes wide gaps or fissures. Important effects sometimes accompany the formation of such accidental cracks and fissures. Whole mountain masses are often shattered, or otherwise affected, and debacles not unfrequently produced.

Beds

A definitely limited rock mass, consisting of the same species of rock throughout, is called a bed, and mountain masses or formations are composed of a succession or superposition of such beds. These beds exhibit one primary difference, having reference to their relations of dimensions: they are either extended with tolerable uniformity in all directions, or else in one direction rather than another. In the first instance the components have a curved surface, or undefined angular form, while in the latter they approximate to the tabular. These beds are sometimes connected over extensive spaces, and sometimes they are interrupted. This interruption is either apparent or actual. The apparent is very interesting in a geological point of view; it especially occurs in trough formations. If we examine the map of the tertiary basin of Paris (pl. 44, fig. 6) and its section (fig. 7), we shall see that the chalk formation is interrupted at Bourges, Auxerre, Chalôns, Rheims, and Laon, by the tertiary masses, disappearing at Paris, Melun, and Orleans, and coming out again at Chartres, Tours, Le Mans, Evreux, Rouen, and Amiens. This, however, is not actually the case; the chalk is only covered by the tertiary, as seen by the section, where 1 indicates the tertiary, 2 the chalk, 3 the succeeding Jura formation. The bed 2 thus forms a trough or basin, in which the bed 1 has been deposited, hiding the other to a certain extent.

The beds are either in immediate contact, or they are more or less separated from one another. In the latter case they are separated by the interposition of an inconsiderable mass. By their mutual contact they are brought into layers, which generally follow a definite order. Before considering this latter point it will be necessary to pay some attention to the mode of bedding.

Beds of tolerably equal dimensions are often bounded by others only on one side; and, again, may be inclosed on all sides. The former then not seldom project from the latter. Most frequently the beds are laid, one on top or after another, forming various angles with the horizon. This condition of imposition or combination is known as the order of succession; thus we say the bed A (pl. 43, fig. 4) succeeds B, B succeeds C, C succeeds D, &c. In fig. 3, also, a succeeds B. The study of this order is of great importance in the consideration of stratified rocks.

When a plane of arrangement is more or less horizontal, and the beds lie one above the other, they are said to be imposed, or to cover one another; if this be not the case, they are applied. When beds come one after the other, we have to examine whether the applied bed lies at an equal, a higher, or a lower level.

When beds are imposed, it not unfrequently happens that they decrease as they ascend, thus giving rise to the formation of terraces like the Trapp Mountain on the Scandinavian peninsula. Overlapping exists when one bed overlies two or more others. Thus, if a bed of muschelkalk rest against one of sandstone, and both be overlaid by a bed of keuper, then the latter is said to overlap the others.

As already mentioned, stratifications are divided into conformable and non-conformable. Conformity may exist either in a parallelism of the planes of stratification (as pl. 43, figs. 3 and 5), or in an equal extension of the strata, as o and a (fig. 3). Non-conformity exists where the strata neither exhibit parallelism nor fall in the same plane, as seen in fig. 6. Here A, B, C, D, have different positions from F and E, although A, B, C, are conformable to each other, as also are F and E.

Order of Succession and Relative Age of Rock Beds

Long continued and careful observation has shown that a constant order exists in the succession of different rocks, and one that is never departed from. This is especially the case with the stratified masses (those formed by successive deposition from water). Thus we find strata of muschelkalk lying on variegated sandstone, and keuper on muschelkalk, and this succession occurs wherever these rocks are found; if they were to be continued round the earth, they would embrace it concentrically, like the coats of an onion. This condition, to a certain extent, would, in fact, have existed, but for the interference of volcanic or volcanoid actions; these have elevated large islands, and even entire continents, from the bottom of the former universal sea, and thus prevented any further deposit on these portions of the ancient ocean bed. It is only where water occupied large basins that this could occur. The strata thus formed we find to be interrupted by non-stratified rocks, these sometimes spreading above them, just like the lava streams of modern times, which, after filling up deep ravines, run over the edges, and are diffused over the surrounding country. The correctness of this analogy is shown, not only in the above relation, but also in the petrographical condition and structure of ancient and modern igneous rocks. It is upon these diversities of existence of the different beds of rocks that the difference between normal and abnormal masses has been grounded (exogenous and endogenous of A. von Humboldt). The former are the really stratified, the latter those which were once in a melted condition. Inasmuch as we are permitted to assume that all normal masses have been deposited from water, we are entitled to consider their order of succession as indicating their relative antiquity; a rock is then older than the one above and younger than the one below it. An absolute determination of the antiquity of strata is impossible, even approximately; this much is, however, certain, that the oldest proclaims an age which vastly exceeds that of 6000 years.

To determine the relative age of masses, which, genetically considered, must be supposed to have been forced up from below, it is necessary to pursue a different method; we cannot, of course, determine from the actual succession in this instance. In this case we must have reference to the penetration of one abnormal mass by another, and that of normal by abnormal. We can estimate the age of one abnormal mass only in reference to another or to a normal. That phenomenon of interpolation is of not unfrequent occurrence, being often seen in some basalts. An instance of this is seen in the Electorate of Hesse, near Eschwege, where a basalt has pierced through the variegated sandstone, and overlies it. This relation has been revealed by an extensive stone-quarry which affords an excellent view of the whole circumstance. The sandstone has been discolored in the vicinity of the basalt, and melted with it at the immediate surface of contact. The basalt is thus newer than the variegated sandstone, or the abnormal younger than the normal. The same is also the case in the Meissner mountains in Hesse, where basalt has broken through the tertiary brown coal, and poured up over the top. The penetration of abnormal masses by others also abnormal, is likewise of frequent occurrence. Thus, in the vicinity of Heidelberg, granite may be seen which is traversed by veins of granite of entirely different petrographical character, of another color and other grain. The granite traversed must necessarily be the older of the two. In volcanic regions, also, we frequently see trachytic rocks traversed by basaltic, or older lavas by younger, as shown in pl. 43, fig. 11. The dark portion is an older abnormal rock, pierced by a younger (the vertically lined portion), and together with the dotted normal elevated by it. The alterations effected by abnormal masses in the stratification of normal cannot readily be mistaken. By the elevation of the former the strata of the latter have been upheaved, broken, and sometimes entirely inverted. Pl. 43, fig. 15, is a profile of a portion of the Hartz mountains, in which a represents the Brocken, consisting of granite, which has upheaved and pierced through the normal transition slate, the individual strata succeeding, each in precisely the same relative order, and of the same size on each side. In this instance, as in many others, it is impossible to overlook the agency of the granite. By means of such elevations older strata are brought to view, and man enabled to ascertain facts with reference to subjacent beds, which must otherwise have remained buried in perpetual obscurity. Did the different layers envelope the earth with the regularity of the coats of an onion, it might be possible to pierce through one, or at most two of these, by mining operations, and no more. In the present condition of things, however, we find an entire succession of rocks revealed, with a limited extent of surface, which otherwise, at depths of entire miles, would have been beyond our ken.

Formations, Groups, and Systems

If we consider the different rock beds, with respect to their constitution, we shall soon find that the most important are represented by only a few species of rocks; limestone, sandstone, clay, and the marls, are those which occur most frequently. Nevertheless, they exhibit such decided characters in their different relations, as to render it impossible to mistake them in certain groups, and to fail of coming to the conclusion that they were formed within a certain definite period of time. These characters have reference to structure, to condition of aggregation, and to the included fossils or organic remains. Such a combination of beds, exhibiting these features, is called a formation.

In such a formation we distinguish with reference to the importance of the included beds; principal measures, which always exist; secondary, which seem to accompany the last, and generally are of no great extent; and subordinate, which do not always occur in the formation, but are limited to restricted spaces here and there. Single series of deposits within a formation, agreeing in more special characters, give rise to another distinction into groups; these, not unfrequently, again being composed of individual rock species, which, in turn, may be built up of strata. On the other hand, entire formations may stand in a certain relation to each other, giving rise to their collocation into systems.

Although a formation or a group generally possesses the same petrographical character in all parts of the earth, yet there may be exceptions in certain cases. Certain groups of strata may be entirely different from others, and yet be of contemporaneous origin. When such an abnormal condition occurs we have to deal with a representative or a geognostical equivalent.

Subordinate Strata

A rock measure is rarely so constituted as to consist entirely of the same geognostical species; measures also frequently occur which must be considered as subordinate, whether standing in a definite structural relation with the primary measures or not. In the former case they lie between the beds of rock connecting them with each other.

The ordinary subordinate beds, or those included between the approximately parallel surfaces, exhibit, in general, the same relations as were found to exist in the case of stratification. Thus certain coals and many iron ores occur in such beds. These are generally of nearly equal dimensions, and approximate in a greater or less degree to the spherical or spheroidal form. Forms of indefinite surface also occur, and this not very rarely.

The ore beds of the north, as the copper and iron pyrites’ beds at Fahlun, the ironstone at Arendal, &c, occur in masses of the above-mentioned character.

Here belong also those matters which fill fissures and clefts in rocks. This matter may be of very different character in different cases; it may have been -introduced by a washing in from above, or by the injection of abnormal matter from below (pl. 53, fig. 14). These two varieties are readily distinguishable. The subordinate beds already considered, all stand in a certain connexion with the rock mass; there are others, however, in which this is not at all the case. These are of various shapes, ellipsoidal, spherical, &c., and vary in size from an inch to many feet. They are either partly or entirely filled up. The masses which fill the spaces frequently have a somewhat definite structure, variously colored layers, conformable to the walls of the cavity, as in pl. 43, fig. 19, or lying horizontally, as in figs. 17 and 18, alternating with each other, and not unfrequently leaving cavities at the centre, which become filled with crystallizations of various mineral substances. The same thing occurs in amygdaloid (fig. 16), a rock containing spherical, a, ellipso-spheroidal, d, almond-shaped, b, cavities, filled with calcareous spar, these varying between the size of a few lines and several inches. Stalactitic formations are also met with in such cavities, as in fig. 17. The contents have most probably been introduced by infiltration. It is well known that water containing carbonic acid gas in solution, can dissolve carbonate of lime, of which calcareous spar consists. This solution, penetrating into the cavity, there deposits its mineral matter. It may be asked whence comes the carbonic acid of the water? The question is not difficult to answer when we recollect that a small proportion, about one volume in 2000, of our atmosphere, consists of carbonic acid gas, which, being dissolved by the descending rain, is brought into contact with calcareous rocks. That water is capable of penetrating solid rocks, is well shown by the amount contained in stone dug out of the ground, unless these be of a glassy character, as is the case with obsidian, pitch-stone, &c. The infiltration of water through the solid roofs of caverns is another instance. Spaces nearly or entirely filled up, sometimes clearly exhibit the point at which the water penetrated. The continuity of the layers is seen to be interrupted at this place, as in figs. 18 and 19; a represents the layers which leave an open tube at d, through which the infiltration took place. Rocks and mineral substances occur in such spaces as subordinate beds of the most different extent and character. The character depends upon the accompanying minerals, some of which, as iron pyrites, copper pyrites, various iron ores, &c., may be advantageously worked by the miner. Small cavities of the kind are called nests. They are either isolated or connected, and not unfrequently stand in such relation to the associated rocks, as to form a continuous succession of beds parallel to the latter.

Veins

Of the subordinate members of various groups of rocks, those deserve particular mention which, while exhibiting a great preponderance of one dimension over the other two, stand in no connexion with the structure of the rock itself. Veins are of this character: they belong to the most important forms exhibited by the earth’s crust, since it is from them that most of the metallic ores and native metals are derived; their interest, however, does not depend entirely on the fact of their containing these useful or valuable substances, but also on the mineralogical beauty of crystallization and form frequently presented by their contents. Veins break through and traverse the stratified and amorphous rocks at various angles, rarely following the lines of stratification or cleavage, and then only for a short distance. There appears to be no regular law to which the course of veins is subjected: they seem to pursue their own course, without being affected in the least by the hindrances which stratification would seem to present. Most mining operations have reference to the following up of veins, as may readily be seen in almost any mine other than one of coal: here the substance sought for always occur in beds, layers, or strata.

The shape of a vein can only be ascertained by working it. Its dimensions in a horizontal direction may thus be determined; but the matter is more difficult with reference to its vertical descent. Little is known of the character of veins at great depths, and this ignorance prevents much knowledge of their true character. The upper portions of veins, however, can be readily investigated; they are either exposed to view at the surface, when the incumbent detritus has been removed, or else they wedge out before coming through the containing rock. The horizontal course of a vein, with reference to the meridian, is known as the direction, and the angle of descent, formed with a vertical plane, is called the hading of the vein. In most cases the vein comes to the surface, where it may project like a wall. In reference to the distribution of the vein, three principal parts are distinguishable, the central and two wings. In a very few cases the vein is everywhere uniform; it is more generally ramified, and runs out into threads. The wings may vanish in a similar manner, although they are sometimes found to be cut off by faults. This cutting off may be effected by dykes of igneous matter or by other veins. In such instances the vein may, in most cases, be recovered on the other side of the displacing body, although not always in the line of continuity.

A vein frequently swells out in parts of its course, so as to occupy a considerable space. The masses filling up these spaces are termed lodes.

The matter filling up a vein is called the matrix or gangue, and may be composed of very different substances. These consist of mineral bodies, of mixtures of mineral species which do not occur as rocks, of true rocks or of their mixtures, either loosely aggregated or cemented by some other substance, thus forming a true breccia. A vein may be filled with a metallic ore, mixed with some non-metalliferous substance, the latter being termed the gangue. While veins containing non-metalliferous matter exclusively are of rare occurrence, it is still more seldom that they are found occupied by native metals. This latter case occurs more frequently in the copper mines of Lake Superior than anywhere else. Gangue, or matrix and ore, are most frequently found together.

The relative ages of veins, as of abnormal rock masses, must be determined by their mutual penetration. Investigations of this kind can only be carried on in extensive mines, and even there the results are by no means satisfactory.

The filling up of the vein is either entire or partial. The former case is peculiar to abnormal masses, such as granite, syenite, diabase, trap, and porphyry. The occurrence of druses is intimately connected with the partial filling of veins. These are hollow spaces of ellipsoidal form, their major plane of intersection parallel to the plane of the vein (pl. 39, fig. 81). They are of different, often very considerable size, and are sometimes lined with the most magnificent crystallizations. A large druse was opened at Andreasberg a few years ago, and brilliantly illuminated with torches. The splendor of the appearance produced by the reflection of light from the thousands of crystal faces is described as having been almost overpowering. Such drusy cavities most generally occur towards the upper extremity of the vein, decreasing in number with the descent.

Ores are said to lie disseminated in the gangue when they are interspersed in small particles, and imbedded when aggregated in larger masses. Gangue and ore may likewise alternate in layers parallel to the sides of the vein, as seen in pl. 43, fig. 20. Here the layer a, immediately lining the cavity of the vein, consists of brown blende; the succeeding one, b, of quartz; the layer c, of fluor spar; d, of brown blende again; e, of barytes: f, of radiated pyrites; g, of barytes; h, of fluor spar; i, of radiated pyrites; k, of calcareous spar; and l, of a drusy cavity, lined with crystals of calcareous spar. In some veins the ores include spheroidal masses of the gangue, so as to present an annular appearance. An argentiferous galena of this character occurs at a mine not far from Klausthal in the Hartz, for the above-mentioned reason called “ring and silver thread.”

The connexion existing between mineral veins and the inclosing rocks is quite different under different circumstances. Sometimes the former separates readily from the latter, either owing to a natural absence of connexion, or to a decomposition and weathering of the outside. At other times the vein mass is so intimately united with the rock as to cause great difficulty in the separation.

When a vein is not precisely perpendicular (a rake vein) it may either hang (form an obtuse angle with the descending vertical) or lie (form an acute angle with the vertical).

A very remarkable relation sometimes exists between the vein mass and the including rock, with respect to their internal and external peculiarities; these relations, however, cannot be combined into any definite system. The principal facts of the kind are, that the vein, on the whole, is weak in proportion to the hardness of the rock; also, that the same vein may continue through different strata, and be of different contents in different rocks, and that the gangue may or may not exhibit an affinity to the rock.

Neighboring veins, which run more or less parallel, communicate only by their ramifications or threads; they may, however, intersect each other at various angles, these being either right or acute and obtuse (pl. 39, figs. 85, 82). The veins sometimes intersect, run together for a short distance, and then separate, as seen in fig. 83.

When such intersections take place it is in most cases possible to distinguish the intersecting from the intersected. A vein, A, cut by a vein, B, sometimes is continued in precisely the same course; it frequently, however, experiences a displacement to one side or the other of the original direction, termed a shift (fig. 84). The continuation of the intersected vein on the opposite side may narrow or expand (fig. 85); it may ramify (fig. 86), the ramifications being sometimes occupied by ore of different richness from that of the rest of the vein. It occurs not unfrequently, that the vein B, crossed by the vein A, is entirely cut off (fig. 87).

Veins sometimes are found which consist of the combination, at every possible angle, of innumerable threads, weaving together entire mountain masses. This is the interlaced vein in which tin ores generally occur.

Theory of Veins

The true character of mineral veins is still involved in great obscurity. There can be no doubt that veins are the filling in of splits, fissures, or cracks, and that the origin of many veins, especially those which occur in abnormal masses, can be satisfactorily explained. The answering of the question, as to how these cracks arose, and in what manner they have been filled up, presents difficulties so great, that a long time must probably elapse before they are entirely removed. Many of the theories suggested are untenable on their very face; and others, not quite so preposterous in themselves, require more satisfactory verification than they have vet received.

The assumption that vein fissures owe their origin to volcanic actions, among which we enumerate earthquakes, and the elevation of plutonic, volcanic, and volcanoid masses, possesses a great show of probability, since entire systems of veins may be reduced to certain points of elevation.

Mount Etna furnishes remarkable illustrations of this kind. The veins belonging to one period of eruption all run more or less radial towards the eruption cone of the principal crater; these veins thus belong to the principal crater. Now there are many systems of veins, in which each vein has reference to the same point, or stands in such similar connexion with certain points, as to compel the supposition that a principal crater must at one time have formed the centre of such a system. The phenomenon is not rare indeed of a volcano so choking up its old crater, as that the molten matter in its elevation has been compelled to throw up a new crater, in connexion with whose formation new systems of cracks make their appearance. This explains the fact that veins are of most frequent occurrence in those primary rocks which are most intimately in communication with abnormal masses; ore veins are also frequently found on the limit between normal and abnormal masses, and are known as contact veins.

The history of the hypotheses adduced to account for the phenomena of veins is much the same with that of the suggestions with reference to the origin of terrestrial volcanoes. The most improbable and exaggerated hypotheses have been propounded in this respect, many of them pure fancies of the imagination, supported on imperfect observations, while others again possess a greater amount of plausibility, and even in some cases establish laws which yet cannot be considered as applicable to all cases. Thus we may, with propriety, assert that veins of calcareous spar in carbonate of lime, veins of gypseous spar in compact, gypsum, &c., have been filled by infiltration from the accompanying rock. This, however, may not be said in regard to metallic ores, or of such veins as contain native metals, since we cannot understand what medium could have dissolved these substances, which, besides, we do not find in the accompanying rock.

The principal theories, according to Von Herder, may be distributed under four heads:

1. Congeneration Theories, which consider the veins as having been formed contemporaneously with the accompanying rock, and not by subsequent filling up. This antiquated view has too much against it to require any special refutation.

2. Theories of Lateral Secretion. According to these the contents of veins are to be considered as leachings or deposits of solutions of the accompanying rock. Metallic substances are supposed to have been deposited from salts or other combinations upon the solid walls of the veins by means of galvanic processes. That the component particles of calc spar, gypsum, talc, and of geolitic and silicious minerals, may have been dissolved in water from the accompanying rock, and deposited as such minerals on the walls of the vein by evaporation of the water, is, as above remarked, very probable; but the occurrence of metallic minerals can hardly be explained in this manner. This theory is thus very one-sided.

3. Theories of Descent. These were earnestly supported by Werner, who endeavored to accommodate all facts to the prevalent Neptunian hypothesis. He considered the vein mass to have been deposited in previously existing cracks, just as the stratified rocks were deposited from water. Single vein masses have unquestionably been formed in this way. but they are of quite unfrequent occurrence. To this view it may be objected, that older and newer, primary and secondary minerals, may be distinguished in the same vein; that it has not yet been proved that all veins wedge out below, the contrary being capable, in many instances, of complete demonstration; that the same matter ought to have been deposited in other situations than in veins alone, which has not been known to occur. Conversions and metamorphoses have unquestionably been produced in the upper portions of veins, by the penetration of small quantities of water, as shown in the formation of carbonate of lead, sulphate of lead, and phosphate of lead, as well as chlorine combinations of lead, from galena, &c. Nevertheless, this theory, thus restricted, is not accepted by the disciples of Werner.

4. Theories of Ascent. These endeavor to prove a filling from below upwards. The ascent may take place in various ways, either by injection, by penetration of the vein mass in a molten condition, by infiltration, bv deposit on the walls from ascending mineral waters, and by the sublimation or deposit of solid particles from a gaseous state of aggregation, produced by a diminished temperature. Formations of this character we may see going on now before our eyes, and especially the sublimation in volcanic operations. It not rarely occurs that cracks which start in lava currents become lined with crystallizations of specular iron, common salt, and sal-ammoniac. The sublimation of galena in stack furnaces, which is deposited in splendid crystals, is a fact of high importance. The infiltration spoken of under this head must, perhaps, be distinguished from lateral secretion; water, indeed, may in great part have leached the accompanying rocks, and have collected at the bottom, there, however, to be heated and driven up. Thus we do not have an immediate lateral secretion, but an ascending infiltration. This has not, indeed, been observed in veins; yet some plausibility is derived from the analogies furnished by the Carlsbad fountains and other springs, which deposit calcareous sinter or hydrated oxyde of iron, as also by the hot springs of Iceland, the Geyser, the Strocker, &c., which deposit silex and chalcedony. These deposits take place not only on the exposed surface, but also on the inner walls of the fountains.

Although some of these theories may be capable of explaining particular phenomena, yet we may not assume that the causes they suggest are the only ones; it is exceedingly probable, that of many agencies, both past and present, which have played and are still playing their part in the bosom of the earth, we are entirely ignorant.

Fossil Organic Remains, their Relation to the Existing Organic World, and their Significance in the Geological Point of View

Petrifactions are organisms more or less perfectly preserved, and partly or entirely converted into stone. It must not be understood, however, that an organic substance has really been transformed into an inorganic, but only that as particles of the former have been removed by decomposition or other causes, their places have become filled by mineral matter. Some, however, must be considered as simple transformations of organic matter, as is shown in the conversion of wood into coal.

Petrifactions in general may be considered:

1. In a natural history point of view, by which they are classified and described. Their most natural classification is that which interpolates the different species of animals and plants into the present zoological and botanical series. As many of them are forms entirely foreign to those which now exist on the surface of the earth, such an arrangement is capable of furnishing the most desirable and interesting conclusions with reference to the development of organic life.

To every one who has been at all occupied with a special study of botany or zoology, the fact will be familiar, that among closely related classes, orders, families, and genera, there occur species which it is difficult to refer to one division rather than to another; species which appear to form the actual transition from one such division to the rest. In other cases the reverse is seen, and groups stand out isolated from ail others; species even occur which are apparently disconnected with their fellows. These gaps, which thus exist in our systems, built up from our knowledge of the present living world, are in a great measure filled up by the fresh material derived from the study of past races. It is not necessary to the character of a fossil remain that actual petrifaction shall have taken place, the bones of animals dug up from caves, or found buried in alluvium, being truly fossil, and yet possessing much the same composition with recent bones. To qualify an object for a place among what are technically called organic remains, it is necessary for it to have become extinct at some time before the historical age of the world. In some cases, however, as in certain species of shells and numerous vertebrata, the same species occurs as living, both before and in the present geological era; in this case their ancient remains are still true fossils. The science which thus treats of long extinct individuals, as well as species, is called Palæontology.

2. The second point of view from which we look at organic remains is the geognostical, inasmuch as they are found in stratified rocks. In these they occur in various forms, sometimes as actual remains, and at others only as casts or impressions of what once existed. The parts of the organism may have vanished, with or without the space vacated having been filled up by mineraf matter. Again, certain cavities originally existing in the object may now be penetrated and occupied by stone. The external shell of the animal, when such existed, is sometimes preserved and sometimes not. The penetrations of inorganic matter occur very frequently, and consist principally of lime, clay, and silex. The penetration of silex is exceedingly interesting, inasmuch as it was frequently produced by infusoria. These animalcula, with their silicious skeletons, and in infinite numbers, probably attacked the soft side of animals, and in dying left their skeletons on the spot. This is very conspicuous in some fossil echinidae, whose calcareous shell incloses a silicious nucleus, which, under the microscope, is found to consist of such organisms. Some parts of organic matters have also experienced alterations, as well by chemical decomposition as by mechanical substitution. An example of such chemical decomposition is found in lignite, which originally consisted of wood. A substitution is often effected by silex; thus we sometimes see entire trunks of trees of it, and not unfrequently one half of a tree or branch replaced by the silex, the other half still continuing to be lignite. This silex, probably, in a dissolved state, permeated the entire tissue, filling up the spaces left by the removal of the organic matter. The pyrites, also, which sometimes lines the cavities of fossils, in all probability, infiltrated the mass in the state of sulphate of iron, and was subsequently converted into the sulphuret. It is well known that decomposing organic matter furnishes powerful means of reduction, by abstracting oxygen, to combine with their own decomposing particles, which are thus converted into various volatile gases. Another mode in which organic bodies occur in the strata of normal rocks, consists in the preservation of some portions and not others. Thus the shells of mollusca are most frequently found without the animals. The organic matter may also have disappeared from these shells, leaving them in a calcined state.

Occurrence of Fossil Remains

Strata are far from always presenting organic remains, these being only found in such as have been deposited from water. It is sufficiently evident that the} cannot occur in igneous rocks, any indications of their existence in such localities being entirely accidental. This, indeed, is sometimes exhibited where abnormal masses stand in immediate contact with normal, and include them. A feature of this kind is seen in Radauthal in the Hartz, where fragments of sandstone, containing impressions of leaves, are inclosed by euphotide.

Organic remains have been found to occupy a definite relation to strata. Thus some are entirely characteristic of certain formations, groups, or systems, and even of individual strata. Certain species and genera are limited to particular localities, while others are of more general occurrence; they are either mixed up or they lie distributed in a regular manner. Animals and plants most generally occur in different strata, the former in limestone, the latter in clay, although this relation is not exclusively maintained. It not seldom occurs that organic remains, as of shells and corals, compose the principal material of entire beds. This is abundantly illustrated in the Silurian system of North America and Europe.

While by far the greater number of fossil remains are evidently very different from the recent, there sometimes occur instances, especially in the newer strata, of extraordinary similarity. They are, however, in most cases specifically different, and of considerably larger size. The few species which have been found, both fossil and recent, are of very great interest to the geologist. While older petrifactions occur quite universally distributed over the surface of the earth, these are found only in restricted localities, so that from them we are entitled to infer a climatic difference. The same general features of climate must have prevailed all over the earth in the earliest periods of her history, nearly the same mean temperature existing at the poles as at the equator, or else there could not have been this uniform distribution of animal and vegetable life. This is, nevertheless, an assumption which is not well established, the reasons both for and against being numerous. A very cogent reason against it is the occurrence of the elephant and rhinoceros frozen up in the ice of Siberia, which were well prepared to resist the cold that is so eminent in that country. A specimen was found in 1799, with the flesh and hair still perfect, and with remains of the arctic coniferæ in its stomach.

Fossils often occur in localities far distant from the places where allied forms now exist in a living state, as shown in the above-mentioned instance of the European elephas, primigenius, or mammoth. Remains of the lion, tiger, hyena, crocodile, monkey, &c., are found in England, France, and Germany, where even allied families hardly occur. A remarkable (and perhaps still problematical) case is furnished by the occurrence of a petrified Juglans cinerea in the Wetterau, the tree being a familiar member of the present flora of North America.

Improvement of Organic Forms with the Increasing Age of the Earth

A little attention to the succession of organisms, as presented by fossiliferous strata, will soon convince us of a progressive improvement and perfection of forms. The most imperfect are found in the oldest strata, and the higher they occur in any formation, the higher the degree of their organization. By this, however, it is not meant that plants existed at first alone, and that after they had attained their highest degree of development, then the lowest animals made their appearance, but rather that the development of the animal and vegetable world took place in two parallel series. The oldest plants and animals stand so closely together, that in many cases it puzzles the most skilful palaeontologist to decide when any given fossil belongs to one or the other.

Neither must we be understood as affirming that the plants and animals, as they at present occur, are the result of an actual development of the lower forms into the higher, the noblest forest trees proceeding by insensible gradations from the minute cryptogamia, and man from the monad. We simply mean that in successive creations, at successive epochs, the new forms were of more highly organized character than the old. And while the general fact may be as just expressed, there are many special exceptions, numerous instances existing where there appears to have been an actual retrogression. Thus at one time the seas of Europe swarmed with enaliosaurians of immense size and high organization; the Ichthyosaurus and Plesiosaurus devastated the marine regions which they inhabited. Yet all traces of this high order of reptilia have vanished from our existing fauna, unless the far-famed sea serpent be a representative, as has been suggested by some zoologists. The gigantic Dinosaurians, too, have vanished; and of the once extensive order of Crocodilians, only a few imperfect forms remain here and there on the surface of the earth.

The oldest plants were probably those belonging to the land, water plants being found long after; that is, in much more recent strata. The case was different with animals, the oldest having been marine.

In the oldest formations acotyledonal plants come first, and then monocotyledonal; a few dicotyledons next occur, subsequently to present themselves in greater number.

Among animals corals are found first, then radiata and Crustacea, and afterwards fishes. Mollusca and radiata then occur more abundantly, and in enormous quantity, and afterwards the most extraordinary and gigantic, reptilia. Subsequently we find mammalia, more rarely birds. Human remains occur only in formations of our era, and which are going on at the present time.

Relation of Palæontology to Geology

It will have been understood from the preceding remarks that palæontology forms one of the most important branches of geology. It is almost indispensable to the accurate determination of strata groups, since the organic creations of certain periods are found to be much more constant, and more generally distributed than the contemporaneous mineral deposits. As we shall see subsequently, sandstone, lime, clay, and marl substance, alternate with each other in the most varied manner; and it would be a matter of the utmost difficulty, nay, of almost absolute impossibility, to decide without the assistance of organic remains, and upon simple petrographical characters, upon the relative age or the identity of strata in different regions of the world. Modifications in the fauna and flora of a certain period of time may, indeed, occur; but this is only in single cases, and especially in the more recent deposits, where, as already remarked, it is impossible to mistake a difference in the external influences on organization.

Object of Geology

The object of geology, in connexion with palæontology, is indeed important, and interesting as important. It seeks to develope the geography of the earth, as it existed at various periods of time, to point out what extent was possessed by the sea, what by the continents, what course was held by rivers and streams, and by what inhabitants peopled. Geology, however, is not merely an interesting subject of study and investigation, it is one of extreme importance to practical life. A rational system of mining is impossible without it, and how necessary is it in an agricultural point of view! To very many sciences and arts it is of most exceeding value.

Special Oreography

Special Oreography treats of the relations and peculiarities of the solid crest of the earth, and of the order in which the different rock species are grouped. The classification into formations, groups, systems, &c., is based on pure experience alone, since the laws prevailing in regard to the composition of the earth’s exterior cannot be developed by hypothesis. This section of geology is naturally subdivided into two parts, one having reference to normal rocks, the other to abnormal.

Normal Rocks

Normal rocks are especially characterized by possessing and exhibiting a definite and regular order of succession, in which we may always distinguish one superimposed or applied stratum or series from another subjacent to it. Normal masses consist partly of isonomic, partly of heteronomic rocks; the former generally prevailing in the older, the latter in the newer formations. A somewhat similar relation exists in the isonomic rocks in which silex or carbonate of lime prevails; the former is generally inferior, the latter superior. In most strata of rocks there is not the least difficulty in determining that they have been deposited from water, especially from sea water; such rocks are called Neptunian. In others, again, this aqueous character is obliterated to a greater or less extent, and for certain reasons we conclude that such have been transformed from their original condition to their present by means of various agencies; such are called metamorphic rocks.

The occurrence of fossil remains is as characteristic of the normal masses as their absence is of the abnormal. They are found in very many of the normal rocks, but following them up from the recent formations to the more ancient, we after a time find that they cease to present themselves. The class of normal deposits falls naturally into three orders, as established by Hausmann: into bottom series, middle series, and top series. Others, as Elie de Beaumont, Sedge wick, Murchison, and others, do not receive this arrangement, not separating the bottom rocks so decidedly from the others, but including them with the transition; the basis of their division would rather be into palaeozoic, secondary, and tertiary.

Bottom Series

The principal character of these rocks consists in their forming the basis upon or against which all the other normal masses rest. They occur as well at great depths as at considerable elevations, either free or covered by other rocks. Their purely chemical formation is unmistakable, for the species composing them are all of crystalline texture; and this character is so universal as to enable us confidently to assert the absence of the bottom series where conglomerates exist. Silicic acid is one of the most predominating ingredients, both in the form of a silicate and of silex. It is combined generally with the oxydes of aluminium, potassium, sodium, calcium, magnesium, iron, and manganese, with them forming micaceous and feldspathic minerals. That the rocks of this division are metamorphic is exceedingly probable; at least we know this to be the case with respect to crystalline limestone, or marble, this occurring in fact as a subordinate mass between the crystalline shales. It must be remembered that the bottom series were most exposed to the influence of the abnormal masses, from resting immediately on them. The frequent eruptions from the heated nucleus of the earth, formerly of much greater extent than at present, appear to have attacked these strata first, filled them with cracks and fissures, and metamorphosed them by the influence of a high temperature. It is also exceedingl) possible that the ascending central heat of the earth, at one time so much more intense at the surface than subsequently, produced great changes in the fine, loose, badly conducting matter deposited from the water. The stratification of bottom rock masses is very decided, and in many cases is effected by micaceous substances. The strata generally stand at considerable angles to the horizon, sometimes nearly perpendicular, and not seldom entirely inverted: fan-shaped and arched strata in every variety also occur. The principal species of rock are gneiss, mica schist or flagstone, chlorite schist, and talc schist. These form the principal mass, and stand more or less in connexion; while the subordinate masses to which steatite, dolomite, and marble belong, are confined to single beds and limited districts. The bottom rock is very rich in mineral substances, as various silicates, metallic oxydes, ores, metals, and metalloids. Of metallic oxydes magnetic iron ore is the most abundant; the ores are generally mixed with arsenic and sulphur; the native metals are gold, silver, and copper; the metalloids principally carbon in the form of graphite and sulphur; this latter of rare occurrence. This rock never contains fossil remains. The occurrence of abnormal masses in it is of especial importance; between these and the mass of the bottom rocks it is often difficult to draw a line of distinction.

A definite order of succession is frequently exhibited among the members of the bottom series, which, however, is not constant. The gneiss is generally the lowest. It occurs in all modifications, in one place as common, in another as granitic; and again, but more rarely, as hornblende or talc gneiss. Its stratification is more or less evident, sometimes partially or entirely curved, sometimes straight. It sometimes exhibits a wood-like structure, depending on an extension of its components, in which case it splits, not into plates, as is most usual, but into pieces like billets of wood. Naumann, who has minutely investigated this feature in gneiss, calls it linear parallelism. The mica schist or flagstone, which generally overlies the gneiss, resembles it closely in its external character. Next to this come chlorite schist and talc slate, either separately or together. Instead of the chlorite schist we frequently have chlorite rock, this generally exhibiting a coarse stratification. These primary masses sometimes run one into the other, in such a manner as to render it difficult to draw the line of distinction; and although generally succeeding each other in the above-mentioned order, yet not unfrequently they alternate.

Subordinate masses of the bottom series are the following:

Hornblende flag and hornblende schist, which run into each other; their place is next to the mica schist, with which they alternate. This is the manner of their occurrence in the St. Gothard, and in several districts in Sweden. The place of the hornblende schist is sometimes assumed by hornblende rock. The stratification of these subordinate masses is not generally so distinct as that of gneiss; the cleavage is, however, so much the more decided, as is beautifully shown in a quarry of hornblende flag near Ruhla in Thuringia.

Hornblende gneiss occurs more rarely, generally existing near the gneiss, and at times even forms independent masses in it. Weiss-stein (Werner) or granulite (a finely granular feldspar), occupying a similar relation to gneiss, occurs in a few localities, particularly in the ore mountains of Saxony.

Less important subordinate members are schorl schist, graphite flag, micaceous iron schist, marble, and dolomite flag. Horn-slate occurs only in a few places, and clay shale connects the bottom rocks with the transition. Steatite forms isolated masses, especially in chlorite and talc slate, with which it is closely allied. Marble and dolomite, although subordinate, are yet very important and conspicuous members. They are either feebly distinct or closely connected together, and sometimes form entire mountains. They occur most generally in chlorite and talc slate, more rarely in clay shale. They have no distinct stratification, but a three-fold cleavage.

The minerals composing the rock species occurring in the bottom series are not unfrequently separated, occasionally in fine crystallizations. Thus we find quartz and feldspar in gneiss, mica in gneiss, and mica schist, as also garnet, actinolite, tremolite, graphite, &c.

Ore beds and veins occur here in the greatest profusion. The various associated mineral species are either separate or in combinations of various kinds. Beds are found of metallic oxydes, as of magnetic and specular iron ore, in Norway, Sweden, Siberia, North America, Brazil, and other places. There are also ores, as of iron and copper pyrites, zincblende, galena, mispickel, &c, this being particularly shown in gneiss, mica schist, and chlorite slate.

The veins are auriferous, in company with quartz and iron pyrites (in hornstohe and gneiss); silver ores, as brittle silver glance, silver glance, antimonial silver, &c., with iron ores, as brown iron ore, specular iron, micaceous iron, &c.

Veins of galena are generally accompanied by calc spar, brown spar, and quartz; veins of copper ores (consisting of copper pyrites, glance copper, and grey copper), by barytes; veins of cobalt and bismuth, by fluor spar, calc spar, and barytes. Furthermore, veins of antimonial glance and tin ore, with mispickel, molybdena, tungsten, scheelite, occur in connexion with fluor spar, apatite, chlorite, &c. Others, again, are met with, without any metallic minerals, as also some which are filled with abnormal masses.

The bottom series is often of considerable extent, and of various external form, dependent upon the petrographical character of the members; upon the influence of continually destructive forces; upon the more or less compound character of the rocks; upon the stratification; and upon the varying situation above the level of the sea.

Where the bottom series is not considerably elevated above the sea, it forms a hilly or mountainous country (as in Sweden, Finland, and North America), in which the waters have excavated deep channels, widening in places into lakes, as may be seen on a large scale in Finland. These excavations follow either the line of direction of the strata, or that of secondary cleavage. When the sea coast consists of strata of the bottom series, it is generally provided with deep indentations, forming the cliffs seen so conspicuously on the coasts of Sweden and Norway. With a greater elevation of the crystalline shale, its forms become more prominent: moderately high, dome-shaped hills, alternate with deeply cut valleys, their slopes provided with rough and rugged rocks. When of Alpine height, this rock exhibits heights, sharp combs (horns, needles, teeth), separated by valleys, whose steep sides run up from immeasurable depths. Transverse valleys, contracting and widening, with terraced slopes, over which dash foaming torrents, divide the heaven-aspiring rocks.

The ground resulting from the weathering of the bottom series varies much with the subjacent stone. That produced from feldspathic rocks, as gneiss, whitestone, &c, furnishes a mixed, loose, and exceedingly fertile soil, highly favorable to vegetation, on account of its richness in potash, soda, and alumina. The case is different with the non-feldspathic crystalline schist: these generally decompose into a sterile, poor soil. Marble and dolomite separate mutually into a [unkonwn] and dolomitic sand, this division being facilitated by a proportion of iron pyrites. The swelling of the latter produced by oxydation, crumbles down the rock with irresistible force.

The bottom series, which not unfrequently form entire mountains and mountain chains, occur in Norway, Sweden, Finland, Great Britain, in the Hartz and Thuringia (only in traces), in the Saxony Erzgebirge, in Bohemia and Moravia, in the Spessart, the Odenwald, the Black Forest, and on the Italian side of the Alps; also, in the Cevennes, in Galicia and Portugal, in middle and western France, in the Pyrenees, the Sierra Nevada, the Northern and Southern Apennines, Hungary, Siebenburgen, and the neighboring region of the Danube. In other countries than Europe, it is found in Asia, from the Ural to Siberia: in the Himalayas and the neighboring mountains. In New Holland and North America, it occurs in great extent.

Middle Series

The essential geognostical character of the middle series consists in its resting on the bottom, and in being covered by the top series. The species composing this series are unquestionably Neptunian, being partly chemical formations of water, and partly mechanical deposits; they thus exhibit both isonomic and heteronomic formations, which, in the vicinity of abnormal masses, have experienced certain modifications. The occurrence of carbonate of lime is one of the principal characteristics of the middle series, hare presenting its highest degree of development. It is either compact limestone or crystalline marble, and of various degrees of purity. It generally contains admixtures of carbonate of magnesia, or of alumina, in greater or less quantity. The presence of the former converted it into dolomite, of the latter into marl; both together, into magnesian marl. Next in quantity and extent to limestone, comes silex.

Various salts, as gypsum, anhydrite, rock salt, carbonate of iron, &c., are very abundant; carbon, also, is extensively distributed, and by its combinations with oxygen and hydrogen, sufficiently proclaims its organic origin. The occurrence of veins, especially of native metals, is less frequent than in the bottom series, decreasing with the distance from the latter. Conglomerates and sandstone are met with more abundantly, and alternate with masses of marl, with occasional beds of clay interposed. The strata are generally more extended than in the bottom series, and saddle and trough formations are of more frequent occurrence.

The middle series, although often existing at considerable heights, more generally occupies the less elevated parts of mountain masses. It is deposited, either conformably or non-conformably, on the bottom series, in the former case passing as gradually into the bottom rocks, as it is sharply distinct in the latter.

Organic remains are found in most members, sometimes existing in such quantity as to have furnished the principal matter of the strata. The greater number of these remains belong to extinct creations, the more recent strata alone exhibiting forms bearing an affinity to the present. The middle series is divisible into a primary, secondary, and tertiary.

Primary Middle, or Transition Rocks

A portion of the palaeozoic group of Elie de Beaumont belongs to this division of our subject. The primary middle separates the bottom series from the floetz, in external appearance having much in common with the former. The more recent transition strata incline still more in character to the floetz. The strata are more oblique in the vicinity of the bottom series than at a greater distance. Conglomerates, with a cement frequently crystalline, alternate with purely chemical products of an imperfectly crystalline or amorphous character. Limestone occurs more conspicuously in the newer beds. This is sometimes in the form of marble and dolomite; found more abundantly, however, in that of limestone and compact magnesian limestone. Carbon is found partly pure, as in anthracite and graphite, and partly combined with oxygen and hydrogen as coal. Metallic minerals occur, but in less abundance, than in the bottom series: of metals there are gold, silver, copper, and mercury;—of metalloids, arsenic and antimony;—of ores, galena, sulphuret of iron, magnetic pyrites, copper pyrites, zincblende, red silver ore, glance antimony, grey copper, and cinnabar;—of oxydes, specular, red, brown, and magnetic, iron ores;—of metallic salts, principally sphærosidrite, and electric calamine. These occur in beds and nests, as also in veins, the latter sometimes of great extent. The number of fossil remains increases with the distance from the bottom series; plants make their appearance in the more recent transition strata, as in the anthracite coal measures, which bear the impress of a damp insular flora. Decided cotyledons are not yet found; acotyledons, however, exist, in abundance. Two formations may be distinguished: the transition slate, and the carboniferous.

Transition-slate Formation. It is this formation which most nearly approximates to the bottom series, so as to exhibit an insensible gradation into it, when their mutual stratification is conformable. The clay slate is here quite characteristic, and presents itself in the most varied modifications, among which chlorite and talcose occur in particular places. Next to this comes grauwacke, as grauwacke shale, along which are arranged sandstone and quartz rock. Compact limestone and dolomite occur here only in proportion to the iloetz. Fossil remains are found only in single beds, and coal is seldom concentrated in large masses. The principal species are:

Clay Slate, as common roof, alum, and calcareous clay slate. Its stratification is very perfect; sometimes entirely straight, sometimes bent in greater or less curves, and again contorted in every imaginable manner, it occasionally traverses whole mountains. It is almost always found in considerable masses, and frequently alternates with the other members of the transition shale, as with chlorite schist, talc slate, grauwacke and grauwacke slate, hornslate, jasper, silicious shale, and quartz rock. In places where no abnormal masses could operate on it, it occurs as slate clay.

Chlorite and Talc Slate, of a character much as in the bottom series. They are nearly allied to schalstein, into which they pass, as also into chlorite and talc flagstone.

Grauwacke, in all its modifications, as the common, fine, small, coarse, and large grain, as slaty, and as grauwacke slate. Sometimes one modification prevails, sometimes another. The colors vary much; grey, however, appears to predominate. Oxyde of iron, penetrating the stone in an ochrey form, gives to it a red coloring. A soil is produced by its decomposition which acts more advantageously on vegetation than clay slate.

Silicious Conglomerate. This passes into grauwacke, and is similarly constituted. It is generally colored red by oxyde of iron.

Sandstone, which passes into quartz rock, and when mixed with mica approaches more or less to mica schist. Its decomposition consists in a mechanical division. It is generally clay or quartz sandstone, and of a light color.

Quartz rock. This not seldom passes into the above-mentioned sandstone. Its colors are white, brown, red, and violet; it imbeds certain rock species of this formation, as silicious shale, clay slate, and some others. It resists weathering very well, on which account it exerts great influence on the form of mountains.

Limestone. This is most generally compact, pure or mixed with silex, of grey or variegated colors, the latter often connected with the presence of corals. Marble sometimes occurs independently, and sometimes connected with compact limestone, into which it passes. It runs into calcareous clay slate and marble flagstone. Nodules of limestone often lie in clay slate, and are frequently ranged in such succession as to form beds by their contact, which, when of great extent and size, form prominent components of mountain masses. Where it alternates with strata of the transition slate, it exhibits a distinct stratification, which is sometimes greatly modified by the presence of mica. Caves abound in it, these being generally lined and ornamented with stalactital and stalagmital matter. Examples are seen in the Baumanns-cave and Biels-cave in the Hartz, the cave of Montserret, not far from Cordona, in Catalonia (pl. 53, fig. 3), and the Grotte des Demoiselles near St. Bauzille du Putoir in the French department of Hérault, fig. 1. This so-called transition limestone often contains nests of red iron ore, of spathic iron, and the brown iron-stone, as also of calamine in company with galena and copper ores.

Dolomite, both in its true crystalline state and as compact magnesian limestone. It is very conspicuous, but limited to restricted areas. It also contains caves, which, however, are not lined with stalactites, but with rhombohedral crystals. Weathering converts it into a loose sandy earth.

The extent of the transition slate rocks is often very considerable, as also is their occasional elevation above the level of the sea. In the Hartz, this elevation is about 2800 feet, in the Black Forest over 4000, and in the Andes nearly 22,000. Where the strata are rather level, the mountain forms are generally more rounded, while with a more vertical position these are much bolder. Clay-talc and chlorite-schist often form widely extended plateaus; and where they are intersected by long valleys, elongated mountain ridges. The sides of the transverse valleys, as the Selkethal in the Hartz, and the Schwarzathal in Thuringia, are commonly beset with rocks. Granular quartz rock and sandstone not unfrequently form rounded mounds, which project above the grauwacke and slate masses. Limestone, at low levels, presents nothing remarkable in its forms; the contrary is, however, the case when it occurs at greater heights; in narrow valleys it forms precipitous rocks, which are more conspicuous than those of gramvacke and clay slate. The exterior of dolomite is very rough. The Lurleyfels near St. Goarshausen, in the valley of the Rhine, consists of grauwacke and clay slate (pl. 53, fig. 5).

In England, where the transition slate occurs in great perfection of development, three systems have been distinguished; the Cambrian, the Silurian, and the Devonian. Hausmann, rejecting the first, only admits the two latter, and characterizes them in the following manner:

a. The older or Silurian System, containing only crystalline species, or those approximating to the crystalline. Here belong the older clay slate, chlorite-schist, and talc-slate. The clay slate is distinguished from the more recent clay-slates, by the presence of a silicate of alumina (chiastolite or andalusite) occurring in innumerable quantities of individual crystals in some localities. Schulz, however, from recent investigations, doubts the validity of this character. The occurrence of andalusite may be closely connected with the penetration of clay slate by granite. Fossils exist only in small quantity, and are restricted to individual beds.

b. The newer or Devonian system, in which the grauwacke, in connexion with silicious conglomerate and quartz rock, generally of a reddish color, is the most conspicuous member. Limestone occurs in single nodules and in connected masses. This system contains a greater abundance of fossil remains than the preceding, both of plants and animals. Three principal divisions may be established: one containing clay and roofing slate in predominance; the second, quartz rock; and the third, grauwacke, with subordinate masses of limestone. The clay slate is often fissured, a striking example of which occurs on the Lahn (pl. 49, fig. 8).

The veins occurring in the Silurian and Devonian systems, of most importance, are: the auriferous; the argentiferous, with red silver ore and antimonial silver, accompanied by arsenic and galena; the hydrargyriferous, with native mercury and cinnabar; the cupriferous, with copper oxydes and salts, combined with quartz and barytes; the plumbiferous, with galena; antimoniferous, with quartz; and pyriferous, with spathic iron. These veins, which are sometimes of great extent, occur principally in the grauwacke and clay slate.

Elie de Beaumont classifies the older strata in quite a different manner. He divides them into a Cambrian, a Silurian, and a Devonian system.

a. The Cambrian system (système Cambrique), according to this eminent geologist, is composed of the strata which rest immediately on the abnormal masses, gneiss, &c., included. It derives its name from the Cambrian mountains in Wales, where it has been particularly studied by Sedgewick. No very conspicuous or decided characters distinguish this system from the Silurian; they are, however, deposited nonconformably, and consist of grauwacke, clay slate, and quartz rock. The limestone, of very dark color and brittle fracture, is in inconsiderable amount, and the clay slate is the same which we have already referred to as containing chiastolite. The rocks rarely contain organic remains, and plainly exhibit the effects of an elevated temperature.

b. The Silurian system (lower grauwacke, terrain ardoisier, système Silurien). We owe our knowledge of this system to the elaborate investigations of Murchison. The petrographical character of the rocks coincides with that of the Cambrian system, although the palaeontological and stratification conditions are different. They are found in complete development in England, and have been divided by Murchison into many groups. Pl. 46, fig. 1, presents a section of the Silurian system. Below all the rest lie the strata of the Cambrian system, A, against which lean those of the Silurian. The lowest group forms the Llandeilo formation, a, consisting of beds of sandstone (10) and fine granular slaty grauwacke, sometimes containing lime concretions. Against this, and of course at a higher geognostical level, rests the Caradoc formation, b, composed of deep red sandstones (7 and 9), penetrated by dirty yellow veins of quartz, alternating with limestone (6 and 8). Then follow the Wenlock strata, c, consisting of clay slate (5) as the principal mass, with richly fossiliferous, dark, and partly crystalline limestone (4). The addition of clay-slate substance carries this Wenlock lime gradually into clay slate. The boundary of this system is formed by the Ludlow formation, d. The lowest bed, consisting of clay slate (3), rests immediately on the Wenlock lime; upon this lies a subcrystalline clayey lime (2), called Aymestry limestone by Murchison, and, with the micaceous lime and clay sandstone containing an abundance of ichthyolites, closing the series.

The thickness of the Llandeilo strata amounts to 1200 feet; of the Caradoc, to 2500; of the Wenlock, to 1000 (1800?); and of the Ludlow, to 1500 (2000?). The entire thickness of the Silurian system in England thus amounts to 6200 feet (7500?).

The strata of the Silurian system, in Brittany, exhibit a peculiar character: they are bent in an undulating manner, so that the land consists of small flat hills, whose heights are formed by sandstone, and the valleys by slate. A section of the country between Rennes and Nantes (pl. 46, fig. 3) will make this sufficiently evident. The undulating layers, a, consist of the sandstones; the slates, b, occupying the troughs of the valleys. Each wave appears to have been produced by the action of the granite, d, in proof of which may be mentioned the metamorphism experienced by the slates lying nearest to it. Many members, occurring in England, in the Silurian system, are entirely wanting in Brittany, such as the Llandeilo flags and the Ludlow rocks. Upon the Cambrian system, A (pl. 46, fig. 2), there rests immediately a coarse silicious conglomerate, of a red color (1), which, from the accurate investigations of May, appears to belong to the Caradoc rocks, with the incumbent greenish quartz sandstone strata (2), the non-fossiliferous limestones (3), and the fossiliferous quartz sandstones. The strata of a bituminous limestone (5), which alternates with black clay slate, and is known as Figuelles limestone, correspond to the limestone masses which occur in England in the Wenlock group.

c. The Devonian System (Old Red Sandstone, Terrain anthraxifère, Système Dévonien). This has likewise been ably investigated by Murchison, who distinguishes three principal subdivisions in England. Fig. 4 is a section of this system as found in England.

The first division, 1, the tile-stone, lies immediately upon the upper strata of the Silurian system. It contains a fine-grained sandstone of decided stratification, so as to admit of being split into fine laminae, serving the purpose of tiles. It passes gradually into the Ludlow rocks, upon which it immediately rests, and with which it has a similar stratification: it contains very many ichthyolites. The second division forms the cornstone, 2, an alternation of variegated marls with sandstones and impure limestones, in which are scattered small concretions resembling grains of corn. The upper division, 3, consists of quartz sandstone, alternating with coarse-grained conglomerates and marls, through which pass inconsiderable beds of coal. The Devonian system attains a thickness of 10,000 feet in the southwest of England.

The transition slate rocks are very rich in springs, both mineral and hot. Their distribution is very extended, being found in Sweden, Norwaw Great Britain, in the Hartz, in Thuringia, Hesse, Wallachia, and Westphalia: in the Rhine mountains, in the Taunus, West Forest, and in part in the Eifel: in Upper Saxony, Bohemia, Silesia, and in the Black Forest, in the chain of the Alps, in Brittany, and other parts of France; in the Pvrenees, the Apennines, in Turkey, Greece, Siebenbiirgen, Poland, Russia, and in Africa, as well as America, both North and South. Their rich development in North America has been ably investigated by the New York geologists. Murchison, in connexion with M. de Verneuil, has published very copious investigations upon these rocks as they occur in Eastern Europe.

The remarkable table mountain at the Cape of Good Hope (Pl. 43, Fig. 26) consists in great part of this rock. The succession of the strata in the Ardennes is very difficult to determine, their features being much obscured by the numerous contortions and undulations (pl. 46, fig. 5). By reason of these flexures, many strata are brought several times to light on a section, so that it would be very erroneous to consider them as so many distinct layers. It is continued in the Rhenish transition rocks, as shown in profile of the section just referred to.

The Silurian system is indicated by S; upon this rests the Devonian, D. it has been broken through by the volcanic mass V, and upheaved on both sides. The more recent Floetz is seen resting against the right side, as the carbonate of lime k, carboniferous sandstone ks, the anthracite st, and the Vosges sandstone Vog. The Eifel, the Hundsrück, Taunus, and the Rothhaar mountain, are heights which form the continuation of the Ardennes. This may be easily followed on the geognostical map, Pl. 46, fig. 6. Single portions of the Devonian rest on the Silurian near Kronenburg, which appear to have stood in connexion with that in the West Forest, and near Dusseldorf. Upon the Devonian there rests a narrow strip of the carboniferous, at Arnsberg the carbonate of lime, at Iserlohn the carboniferous sandstone, and at Hattingen and Muhlheim the stone coal, which is also seen at Kaiserslautern. Next follows the Trias, which begins not far from Brilon, passes by a small strip of the Devonian in the vicinity of Marburg and Giessen, and end’s to the north of Homburg. It again appears at Bittburg. Single portions of the Vosges sandstone occur at St. Wendel and to the northeast of Birkenfeld. Then follow chalk rocks, which occur in the north at Bochum. Their place is supplied in the south by tertiary masses at Wiesbaden and Mayence, in the west not far from Bonn and Gemünd, upon which rest alluvial masses at Frankfort, Darmstadt, and Diisseldorf. Volcanic masses break through the strata at Andernach and Coblentz, as also in Siebingebiirge, and in the West Forest.

The other side of the Ardennes appears to be formed of the Hartz and the Thüringerwald, a geological chart of which is presented in fig. 9. The Hartz, whose greater part consists of grauwacke, is broken through in the middle by granite, and by small masses of porphyry, which play a greater part in the Thiiringerwald. The transition limestone is not inconsiderable in the Hartz, and constitutes at Grund and Riibeland entire mountains belonging to the Devonian system. In proportion as we recede from the Hartz, the strata become more recent: we pass over the carboniferous, the todtliegende, the zechstein, the variegated sandstones, the muschelkalk, the keuper, the lias, the oolite, the quadersandstone, the chalk, tertiary masses, and diluvium. The same order of succession may also be followed from the Thüringerwald.

Fossils of the Transition Slate Rocks. The fossils of the Silurian and Devonian nearly all belong to forms different from those of the present era. Some of the most characteristic are figured on pl. 37, principally after Elie de Beaumont.

Stromatopora concentrica (fig. 1) exhibits a corolla with fine furrow distributed concentrically on a spherical surface. Tragos acetabulum (fig. 2), similar to the last, cup-shaped, with irregular pits. Syringopara bifurcata (fig. 3), Catenipora escaroides (fig. 4), C. labyrinthica (pl. 42, fig. 65). The Syringopara are distinguished from ihe Catenipora by the position of the tubes in which the polyps lived. In both, these are straight; but while those of the former ramify, and have internal walls, those of the latter are arranged singly one after the other; their extremities forming chain or net-like figures. Aulopora is a somewhat similar genus, of which A. serpens (pl. 37, fig. 7) is of most frequent occurrence. The small tubular cavities are combined in a reticulation, by which they are distinguished from the preceding. Cyathophyllæ and Astrasœæ are also somewhat similar: while, however, the former grow up separately, and may even ramify, in the latter the individual portions are fused together. Pl. 37, fig. 5, represents Cyathophyllum cæspitosum; pl. 42, fig. 64, C. hexagonum; pl. 37, fig. 6, Astrcæa ananas; and pl. 42, fig. 66, A. porosa. These corals generally occur in associations forming large blocks; others, again, as the Reteporae, Gorgonias, and Favosites, are different in this respect. These are free, and consist of imbricated tubes, communicating by pores. Here belong: Favosites polymorpha, (pl. 37, fig. 8), Retepora infundibulum (fig. 9), and Gorgonia assimilis (fig. 10). The first star fishes were not free, like those of the present day, but were supported centrally on a jointed stem. A most interesting relation exists between the structure of the fossil Echinoderms and the embryological character of those of the present day. The succession of extinct and fossil forms is beautifully typified in the changes which the existing species of allied families pass through in their progress from the ovum to the adult. The oldest Echinoderms known in Palaeontology, are the Cystideæ, these being at the same time the most imperfect. They appear as spherical, armless bodies covered with plates, with an oral aperture on the upper part, an anal on the side, and fixed to the ground by a jointed stem. Then come the Crinoids, fixed like the last, but provided with jointed arms, whose motions sufficed to introduce food into the central mouth. Next appear the Ophiuras, animals with arms like the Crinoids, and fixed when young to a stem or pedicle, from which they become free when adult. Finally, we have the Asteroids, which immediately after birth possess arms and a free motion. The Cystideæ occur in the transition rocks, but very rarely. Crinoids are more abundant. Of these, the individual fossils, as well as larger portions of the arms and stems, are frequently found and known as encrinital joints or bones. The crowns, however, are more rarely met with, and the cause of the separation of the parts is probably to be ascribed to the rapid decomposition of the integuments and consequent dispersion of the portions, produced by death. Pl. 37 represents Hypanthocrinus decorus, fig. 11, Cyatkocrinus pyriformis, fig. 12, Dimerocrinus isodactylus, fig. 13. and Cupressocrinus crassus, fig. 14.

Mollusca are of frequent occurrence in the transition slate. Of course the shells alone are found, the soft parts too readily undergoing decomposition. The hinged bivalves belong to the Acephala or Conchifera; the single unilocular shells to the Gasteropoda. The chambered shells are referable to the Cephalopoda, or cuttle fish order.

The Acephalous Mollusca have a soft mucous body inclosed by a mantle which secretes on both sides a calcareous shell inclosing the animal. The shells are connected at the back by a hinge, more or less toothed. The hinges exhibit differences sufficient to furnish excellent distinctive characters. The shells are united by muscles, by means of which the animal can shut them at pleasure. The Acephala are divided into Monomyaria and Dimyaria, as the shell has one or two closing muscles.

The Monomyaria occur in but slight development in the transition slate, the Ostraceæ being entirely wanting, while traces of the Pectinidæ are exceedingly rare. The Aviculaceæ are of more decided occurrence; of these Avicula lineata (pl. 37, fig. 15) is the most abundant. The Aviculæ have an oblique shell, with an acute process of the hinge, which carries a small tooth.

The Dimyaria are found in great variety, and are especially represented by the Cardiaceæ. These have thick, equal valves, with irregular cardinal teeth, and strong muscular impressions connected with the more or less spherical external form. Cardium lyelli (pl. 37, fig. 16), C. pectunculoides (fig. 17), and C. vilmarense (fig. 18). Cypricardiæ belonging to the same family, differ in having oblong inequilateral valves. They have two to three principal cardinal teeth, the preceding genus having four. Pl. 37, fig. 19^a, represents Cypricardia impressa. Among Acephala the Brachiopoda are particularly abundant; they here attain their greatest development, decreasing more and more in number and variety in the more recent formations. They are bivalve, but recognisable by the inequality of the two valves, one being much larger than the other. The genus Pentamerus, to which belongs P. knightii (pl. 37, fig. 19^b, and pl. 42, fig. 62), has strongly curved beaks, and in the interior five longitudinal chambers, two in one valve and three in the other, formed by projecting longitudinal plates.

The Strygocephala have an undulating hinge margin, over which the beak of the larger valve projects. A more or less regular triangular space, the hinge space, is thus formed, which is pierced by a triangular perforation, contracting with age, and becoming at last completely closed. Pl. 37, fig. 20, represents Strygocephalus burtini from before, and fig. 21 from the side. Leptæna is an allied form, with the hinge margin straight, the beaks very close, and the cardinal area very small and without perforation; Leptæna lata (sarcinulata, pl. 37, fig. 22). The species of the genus Orthis have in general the same structure as Leptæna; they are distinguished by the presence of a perforation in the cardinal area; Orthis lepis (fig. 23). The Spirifers have a straight or curved hinge margin, cardinal area large, with a large triangular aperture and bent beaks. The species Spirifer radiatus (fig. 24^a) and S. speciosus (fig. 25), are very characteristic of the transition strata. The very distinct Terebratulæ are found in great abundance in nearly all fossiliferous strata. The beak of the larger valve is provided with a round aperture, through which passes the attaching ligament; under this lies the triangular cardinal area, bordering beneath on the cardinal margin. The most common species are Terabratula ferita (pl. 37, fig. 26), T. wilsonii (figs. 27 and 28), affinis (pl. 42, fig. 59), crispata (pl. 37, fig. 29), and imbricata (fig. 30). In the Devonian System we have Caceola sandalina of conical shape, provided with an operculum beneath (figs. 31 and 32); also Producta depressa (pl. 42, fig. 58).

The Gasteropoda are readily distinguished from the preceding by their external form. The shells of this family are twisted from left to right (dextral), sometimes, however, in the opposite direction (sinistral), and generally consist of one, rarely of two valves. In them we distinguish an apex and a base, in the latter of which is the orifice through which the animal protrudes itself. The axis around which the spiral cone is wound is called the columella or spindle; this is generally solid; when hollow, the aperture of the space included, is called the umbilicus. Some gasteropods possess an operculum by which the opening can be closed after the retreating animal.

The family of Turbinites is characterized by a turriform, conically wound shell, with the mouth entire and rounded. The columella is curved, and ends in a small open umbilicus. The species of the genus Turbo have mostly beautifully ornamented shells. The most important species is Turbo squamiferus (pl. 37, fig. 33). Monodonta is allied to Turbo; in this genus the columella ends at the aperture in a projection or tooth: Monodonta purpurea (fig. 34). The genus Natica also belongs here; its species have the spire depressed, the aperture ovate, with a trenchant right border, a callosity masking the umbilicus: N. subcostata. Pleurotomaria has a conical spire with oblique oval aperture; P. defrancei (fig. 35), P. llovdii (fig. 36). Euomphalus possesses an inconsiderable spire, sometimes none at all; the aperture perfect, with angular border; umbilicus smooth: E. rugosus (fig. 37), E. discors (pl. 42, fig. 57), E. serpula (pl. 37, fig. 38). Cirrhus is distinguished from the preceding by the conical elevation of the spire, C. leonhardii (pl. 37, fig. 39); in Schizostoma the turns of the spire lie in a plane, & radiata (fig. 30). Among the gasteropods, with twisted columella and without umbilicus, belong Buccinum: B. aculeatum (fig. 41), and Murchisonia, differing from the last in the oblique oblong aperture, ending in a short canal, and by the ridge which follows the windings: M. coronata (pl. 37, fig. 42). Bellerophon has a shell curved like Nautilus, the last winding entirely concealing all the rest; it is, however, not divided into chambers, neither does it possess a sipho: Bellerophon bilobatus (fig. 43). Gasteropods also occur without a twisted or curved shell, as in Conulara: C. gervillei (fig. 44). They are tri- or quadrilateral, and narrow above. The half-closed mouth is placed in the base.

The Cephalopoda stand at the head of the Mollusca in respect to their organization. The head, which is furnished with two well formed eyes, is distinct from the body. The mouth is placed in a depression of the head, and contains two strong jaws bearing a somewhat striking resemblance to the beak of a parrot. It is surrounded by a variable number of long muscular arms, serving the purposes of prehension, for which they are well calculated by reason of the numerous sucking disks on their inner face: these suckers are sometimes still further armed by formidable hooks. In the intestines there exists a sac filled with an inky fluid, and which in some cases has with its contents been preserved in a fossil state. This fossil sepia or India ink has even been used to delineate the fossil remains with which it was associated. The Sepiae of the present day rarely have external shells; the animal, however, incloses a solid shelly axis, known in the arts as cuttle fish bone (ossa sepias). The analogous parts of somewhat similar fossil forms are frequently met with in fossiliferous strata. Only two of the families into which the Cephalopoda are divided, occur in the transition series: the Nautilidæ and Ammonitidæ. These have chambered shells, the last chamber of which was inhabited by the animal. The young individual formed only one cell, others being successively added, and the last built being the only one occupied. A membranous tube called the sipho passed through to the last chamber, and was connected as to its function with the rising or sinking of the animal in the water. The position of the sipho, whether passing through the middle of the partitions, along the ventral or along the dorsal, characterizes the subdivisions of the chambered cephalopods.

The aggregation of chambers is sometimes in a straight line, widening above, as in Orthoceras; of this genus, O. attenuatum (fig. 45) and O. annulatum (pl. 42, fig. 63) are of most frequent occurrence in the transition. The partitions are slightly concave, the sipho passing through the middle, Phragmoceras has a structure somewhat similar, except in being slightly curved below into a horn shape: P. ventricosum (pl. 37, fig. 46). They only occur in the transition state. Lituites is rolled up, yet without any contact of the windings: L. giganteus (fig. 47).

The Ammonitidæ are distinguished from the Nautilidæ by the more or less undulating or zigzag character of the partitions, whose extremities are very distinct externally. The sipho lies nearer the dorsal side. In the Nautilidæ the partitions are simply curved with the sipho in the middle or nearer the ventral side. Here belongs Goniatiles, as G. hoeninghausi (pl. 37, figs. 48 and 49), and G. costulatus (fig. 50 and 51).

The class Crustacea is represented in the oldest fossiliferous strata by a very remarkable form, that of the Trilobites. No adult crustacean of the present day is at all similar to the Trilobites: a very striking resemblance is, however, found in the embryo of some recent species. The body of the animal was divided into three principal portions, a head, a thorax, and tail; these were covered by a thin granular or spinous shell, which has rarely been preserved, casts only of these portions being generally exhibited. The head is occupied by a large shield, with a large eye on each side: these may sometimes be recognised as compound by means of numerous facets. The thorax consists of a central longitudinal ridge, with a furrow on each side, and is divided transversely into jointed rings, the number varying from 5 to 20. The caudal shield is divided into similar rings, the central elevation of the thorax being lost in it. Some genera were able to roll themselves up like the genus Oniscus by means of these rings. Striking forms of trilobites are Trinucleus granulatus (fig. 52). Calymene blumenbachii (figs. 53 and 54. and pl. 42, fig. 60). Phacops downingiæ (pl. 37, fig. 55.) Brontes fiabellifer (fig. 56), and the curiously spinous Arges armatus (fig. 57) and Asaphus buchii (pl. 42, fig. 61). Trilobites occur in the silurian of North America in great numbers, both of individuals and species. Some of these are distinguished for their enormous size, as Isoteles maximus, which has been found in Ohio nearly two feet long and more than one foot wide.

Remains of fossil fishes first occur in the transition slate, and of the most singular and unique character. The characteristic form is that of the Cephalaspides, as Cephalaspis lyelli (pl. 37 fig. 58), and Ptericlithys latus (fig. 59.)

Carboniferous Group (Système houillier, Terrain houillier). The most important rock species occurring in the carboniferous are grauwacke, silicious conglomerate, sandstone, quartz rock, and limestone, which, in their petrographical character, are often so similar to those of the transition slates, as to be entirely undistinguishable in hand specimens. There is, however, a great difference in the occurrence of clay masses. Thus while in the preceding formation clay exists as clay slate and burning slate, in the present it is found as slaty clay, thus of much less consistence. The strata are generally much more extended, and form wide troughs and saddles. In some places they have been subject to considerable changes of position, being bent, curved, contorted, &c., in the most complicated manner: in others, again, the greatest regularity is perceivable. The most important metallic salt is the carbonate of iron. Fossils enter in large number, some of them coinciding with those of the transition slate. The carboniferous system is more restricted than that of the preceding, and rarely occupies high levels. In this system three principal groups may be distinguished.

a. Carboniferous or Mountain Limestone (Encrinital limestone), with the principal rock species, limestone and dolomite; these occur partly crystalline, partly compact and of a prevailing grey color. The mountain limestone forms large masses as well as subordinate beds. The cleavage is quite decided, and sometimes gives rise to the formation of caves. It is often very bituminous, the bitumen being sometimes concentrated in single places. The caves often contain tertiary deposits imbedding the bones of terrestrial mammalia. Nodulous masses or concretions of hornstone often exist in the strata. Slate clay and sandstone occasionally alternate with the limestone. Veins occur much less conspicuously than in the transition slate: those of galena, in company with fluor spar, barytes, and elalerite, are most frequent. The fossils are generally animal. This group abounds in springs.

b. Millstone Grit (Flotzleerer Sandstein). This contains principally conglomerates and sandstones, of which silicious conglomerates, grauwacke clay, and quartz sandstone of a grey color, are the most abundant. They are accompanied by a finely laminated, very bituminous limestone, clay-roofing-, alum- and burning slate, as also by silicious shale, jasper, and subordinate beds of bituminous and anthracite coal. Argillaceous sphserosiderite is found in considerable quantity.

c. The Coal Formation proper. This is of great importance, as containing the true coal measures. Stone coal is indeed a subordinate, but yet a very prominent member. The principal mass is formed by conglomerates and carboniferous sandstones: of the former granitic and silicious conglomerates are the most important; of the latter, clay, marl, and quartz sandstones. Accompanying and subordinate masses are: limestone, marl, loam, marl clay, and potter’s clay, which are generally very bituminous, as also a grey slate clay, bituminous shale, drawing slate, amd various modifications of coal. The thickness of this group varies considerably, rarely however exceeding about 900 feet. The strata are rather horizontal than otherwise, although there are sometimes very great irregularities of position. The coarser conglomerates generally occupy the lower levels; the finer, the higher. A similar relation occurs between anthracite and bituminous coal; the former occupying the lower, and the latter the higher measures. The coal beds are generally only a few feet thick. The thickest known are those of Fimini (33 to 40 feet), and those if Dudley in England (33 feet).

The cleavages of the coal are generally distinct, and cut each other at right angles. The roof and floor of the bed generally consist of clay shale. Nodular masses of arsenical and iron pyrites, argillaceous carbonate of iron or sphasrosiderite, galena, zincblende, are sometimes collected in larger or smaller quantity. The occurrence of native mercury, amalgam, cinnabar, and horn quicksilver in coal measures, is exceedingly remarkable: these bodies concentrate in nests and are thus found in loam. Organic remains are met with in extraordinary abundance, being principally confined, however, to plants : animal forms are much rarer (mostly fresh water mollusca): fishes are nearly wanting. Such remains are generally in excellent preservation, especially when they lie in the very fine shales. Jn these the finest nervures of the leaves are sometimes retained. Coal itself is entirely composed of transformed vegetable matter, as is abundantly shown by microscopic and other investigations. Springs abound in the carboniferous system, particularly those containing iron and salts of sulphuric acid. The true stone coal group is very extensively distributed: it occurs of great extent in Great Britain, Belgium, in the vicinity of Aix la Chapelle and Eschweiler, about Saarbruck and in the trans-Rhenish Palatinate; on the borders of the Hartz in less quantity, more abundantly in Thuringia; also in Saxony, Moravia, and Silesia; in extensive districts in France, some portions of Spain, Portugal, North America, China, Japan, and New Holland.

One of the most considerable coal basins is that of the Palatinate, which is about forty-four miles long, and from seven to thirteen miles broad. It rests nonconformably upon the transition slate rocks, while it is covered by Vosges sandstone and alluvium. Pl. 46, fig. 8, is a section of this field: K indicates the coal strata, V the Vosges sandstone, and A the alluvium. This field is often broken through by various porphyries, causing a disturbance of the strata. The amount of coal is very small in proportion to the extent of the basin. It is only in two places, to the north on the Glan and to the south near Saarbriick, that the yield repays the expense of mining. The most important bed is about thirteen feet thick. The English coal formation is more extended, and by the abundance of coal exercises a great influence upon the production of iron. Much of the English iron is derived from sphaerosiderite (carbonate of iron), which occurs in large quantities in the carboniferous system, and even in the coal measures themselves, so that the same mine may furnish both ore and fuel. It is to this, above all. that the cheapness of the English iron is owing. Pl. 46, fig. 7, represents the succession of strata in the English coal formation. It there rests immediately on the Devonian, a, against which leans the mountain limestone, b; next come the strata of the millstone grit, c, which are covered by the lower coal beds, d, containing a large amount of iron-stone; next by the main coal, e, and the upper coal, f, combined with the fresh water limestone. The latter concludes the series, which is succeeded immediately by members of the Permian and new red sandstone.

No country possesses a larger amount of coal than North America, and in none is it found more extensively distributed. It occurs in Nova Scotia, New Brunswick, Massachusetts, Connecticut, Rhode Island, Pennsylvania on both sides of the Alleghanies, Virginia, Maryland, Ohio, and several others of the Western States. Among the most remarkable of these localities are the anthracite beds of eastern Pennsylvania. They are not constituted of the mineralogical species anthracite, but of a variety of common coal containing very little bitumen, and burning with little smoke and flame. This variety occurs in three basins: the Wyoming, the Schuylkill, and the Lehigh. The former is nearly seventy miles long and about five broad, occupying part of the valley of the Susquehanna river.

Fossils of the Carboniferous Period. As already mentioned, vegetable remains are most conspicuous in the coal strata, particularly the vascular cryptogamia, such as Equisetacese, Filices, and Lycopodiaceæ, of sizes far exceeding those attained by modern members of the same families. Among the Equisetacese belong the Catamites, with straight cylindrical branches and high jointed stems. They are striated longitudinally, some with a sheath going round the stem, as in the common Equisetum or horsetail, and others without it. The largest known remains must have belonged to individuals more than a foot in diameter. Such, for example, is Calamites approximatus. These gigantic forms sufficiently indicate that certain agencies were at work in the earlier periods of the earth's history, which favored the development of vegetation to an enormous degree.

The different parts of many species of Filicoid plants, as ferns, &c., occur in great quantity: entire stems and leaves of arborescent ferns are found, and it is probable that the great mass of coal has been produced by accumulations of such ferns. Ferns have cylindrical stems, inclosed by circlets of leaves. When these fall off they leave scars behind them, of a lenticulai shape, and higher than broad; when the leaves are extended transversely they never embrace the stem as in monocotyledons. The woody vessels which pass from the stem into the petioles, form regular and characteristic figures. The leaf scars are in parallel longitudinal rows. The stem supports a crown of simply or doubly pinnate leaves. The only possible means which we have at our command for classifying fossil ferns consists in the arrangement of the nervures.

Sphenopteris has bi- or tri-pinnate leaves, with leaflets distinct, deeply lobed, and the nervures radiating nearly from the base. S. Schlotheimii (pl. 37, fig. 60) is especially abundant in the Saarbrück coal beds.

The bipinnate fronds of Odontopteris have thin leaflets, adherent by their entire base, which is never contracted, nervatures simple or dichotomous, all equal, proceeding from the rachis; central nervure indistinct: O. minor (pl. 37, fig. 61).

The coal strata are filled with vast quantities of gigantic stems of ferns; they have been found over 40 feet long and a foot in diameter. Their leaf scars are in parallel longitudinal rows, but are in much larger quantity than others in allied forms. Their thin carbonized bark readily falls off, exhibiting the casts of the scars. These are known as Sigillaria, of which a stem is figured in fig. 62; fig. 63 is a piece of the same with the bark removed; fig. 64, an enlarged view of the leaf scars both above and below, or within and without the bark.

Stems of Lycopodiaceæ are also found, hardly yielding in dimensions to those of Sigillaria. Thus we have Lepidodendron distinguished from the last by the spiral arrangement of the rhomboidal leaf scars. An entire stem of L. elegans (fig. 65) has been brought to light in the Bohemian coal mines: fig. 66 exhibits the arrangement of the leaves: fig. 67, the scars themselves.

The coal formation, as far as known, is destitute of true dicotyledons; doubtful forms, however, occur, which may or may not be such, as Sphenophyllum annulatum (fig. 68), and Annularia fertilis (fig. 69).

The general character of the invertebrate fauna coincides with that of the transition; nearly the same families and genera occur, although the species are mostly specifically distinct.

In the lower group of the carboniferous system, the mountain limestone, entire strata are filled with crinoidal joints, belonging principally to Rhodocrinites verus (fig. 70, a, b), and to Cupressocrinus crassus (fig. 71, a, b). Here and there are found pelvic fragments of Platycrinus Icevis (pl. 42, fig. 41), Actinocrinus triginta-digitalis (fig. 42), and a form nearly allied to the crinoidea, Pentremites ellipticus (fig. 43). These strata have consequently received the name of encrinital or entrochital limestone. The principal mollusca are Pleurorhynchus minor (pl. 42, fig. 44), Spirifer striata (fig. 46), Producta punctata (fig. 47), Terebratula acuminata (fig. 56), Bellerophon bisulcus (fig. 50), a Pleurotomaria (fig. 51), Euomphalus pentangulatus (fig. 52): of Cephalopoda, Orthocera breynh (fig. 45), Ammonites listeri (fig. 48), Ammonites striatus (fig. 49); of corals, Syringopora geniculata (fig. 53), and Favosites capillaris (fig. 54); of trilobites, Asaphus gemmuliferus (fig. 55).

The vertebrate sub-kingdom is represented by a few remains of fishes, principally teeth, belonging to the Hybodontes. Pl. 37, fig. 72, represents a tooth of Cladodus marginatus.

Various hypotheses have been suggested as to the origin of the coal beds. Some of these suppose an accumulation of drift-wood, and others that the vegetation was produced in the spot where the coal is now found.

The latter assumption appears the more probable of the two, demanding, however, a greater length of time, although not so great as would perhaps be required at the present day. The most convincing proof of the indigenous origin of at least many of the coal beds is found in the fact, that tree-stems are found standing upright in sandstone strata of the carboniferous, at right angles to the stratification, and partly carbonized, partly pyritized. In some places it may be clearly seen that the roots of such stems were implanted in beds of slate clay. A curious instance of this is found in a coal mine near Treuil, not far from St. Etienne, as shown in pl. 52, fig. 7. The upper beds are of sandstone, in which are contained the erect stems; beneath this is a deposit of argillaceous iron-stone, resting on a bed of shale; the whole lies above the coal bed. Similar phenomena are found in various other coal mines.

Secondary Middle Series

This follows immediately after the carboniferous system, and is covered by the tertiary middle. Crystalline masses are here in but slight amount, and stand in decided connexion with abnormal formations. Clay, marl, lime, and sandstone masses here attain a high degree of development. They frequently alternate with each other, and occur in all modifications. Single coarse conglomerates present themselves only in restricted localities. The clay, lime, and marl masses are generally colored by carbonaceous matter, although sometimes they arc of a pure white. Coal is of rare occurrence, as also is that of metallic minerals. Veins are sparingly distributed, and hardly worth following up; karstenite or anhydrite, gypsum, and rock salt, are of more importance.

The secondary middle series or Floetz is very rich in fossil remains, these occurring both in vast numbers of individuals and of species. Forms of the animal kingdom exhibit a great preponderance over the vegetable. The former are principally aquatic, as mollusca, fishes, and reptiles, the latter of colossal size and wonderful forms. Among the few plants dicotyledons are of decided occurrence.

The Floetz generally occupies low levels, with strata more or less horizontal, and is divided into four formations. It has the most extended distribution of all the members of the middle series.

Copper-slate formation (Permian System. Penceian System. Magnesian Limestone). This, according to Elie de Beaumont, likewise belongs to the palaeozoic rocks, and embraces the red sandstone, the zechstein. and the rauhkalk. The principal rock species consist of various conglomerates and sandstones, the former predominating, and generally of red color; also marl, limestone, and dolomite, mostly bituminous; gypsum and karstenite, all of which, although not principal masses, are yet very conspicuous. Carbonate of iron and oxyde of iron are subordinates. Veins are much less in number than in the carboniferous system; a few inconsiderable beds of copper, cobalt nickel, bismuth, and molybdenum ores also occur. This first formation possesses the fewest fossil remains of all the floetz. The diminutive Flora approximates to that of the carboniferous, but differs in the decided presence of dicotyledons. Orthoceratites and trilobites here find their limit; fishes of the ganoid type become more abundant, as also reptiles. This copper slate formation is, on the whole, not abundant, and only in few cases takes a high stand among rocks. It is divisible into two groups; an under, the red sandstone, and an upper, the old floetz limestone.

a. Red Sandstone (Todtliegende). This consists of coarse and fine conglomerates and sandstones of red or reddish-brown color. White or grey sandstones sometimes occur, which then occupy the upper regions of the group. Upon this distinction of color rests the distinction made by the German miners into red, grey, and white sandstone (liegende) which are found to exist in this order.

The conglomerates met with are granitic, argillaceo-ferruginous, silicious, porphyritic conglomerates, and grauwacke. The sandstones: iron-clay, clay, and marl sandstones. An accompanying deposit is formed by red or grey limestone, which not rarely alternates with iron clay.

The conglomerates and sandstones in general present nothing remarkable in their exterior; where deep valleys or ravines intersect the mountain ridges, they produce the most singular rock forms.

The stratification is generally very decided and of great extent in the coarse conglomerates. The cleavage, not very regular, often produces a columnar structure. The situation of the strata is generally horizontal, although sometimes inclined, especially in the vicinity of abnormal masses.

The grey sandstone is noticeable for sometimes containing ores of copper; these are the copper sand ores mined on the west side of the Ural. Fossils are rare, and limited to a few dicotyledonous trees, which occur in the form of silicified wood, whole trunks being sometimes found.

The soil arising from the red sandstones of this group is reddish-brown, ferruginous clayey, and very fertile. This property is sometimes increased by the abundance of springs.

The new red sandstone in the Hartz (pl. 46, fig. 9) lies immediately on the strata of the Devonian system, and is covered by the Zechstein. It occurs in greater masses in Scotland, in England, in Thuringia, near Richelsdorf in the electorate of Hesse, in the Wetterau, the Spessart, the trans-rhenish Palatinate, the Black Forest, in Saxony, the Tyrol, the Vosges. in Russia, in the Caucasus, and in North and South America.

b. Old Floetz Limestone. The principal rock species are bituminous marl shale, compact limestone, magnesian limestone, dolomite, and fœtid limestone. Accompanying species are clay masses, gypsum, karstenite, and rock salt. Where the group is complete, two subdivisions may be distinguished.

The lower division is strikingly characterized by the copper slate, a bituminous marl slate impregnated with copper ores. The proportion of copper is generally small, from one to four per cent. The ores are finely disseminated, rarely collected in mass; they consist of copper pyrites, glance copper, grey copper, iron pyrites, zincblende, arsenical cobalt, and molybdenum glance. From the decomposition of these minerals, various metallic salts, as verdigris and mountain blue, are produced. The strata of copper slate are not generally thick; from one to two, rarely three feet. The thinness of the strata renders it a very laborious matter to mine the copper, the workmen being obliged to lie upon the side or back while extracting the ores. Fossil remains, especially of fishes, abound, owing perhaps to the fact that the great proportion of bitumen has facilitated preservation.

Upon this copper slate rests a fœtid marl, intermediate between copper slate and zechstein. The thickness of the bed varies from four to eight feet. Next comes the zechstein. a bituminous, marly, compact limestone, of brittle fracture, containing clay concretions and drusy cavities. It includes subordinate masses of gypsum, lithomarge, and copper ores, the latter accompanied by the usual salts of copper. The stratification of the zechstein is very distinct, and the rock is traversed by a doubly-rectangular cleavage.

The upper division is exceedingly complicated, and thus difficult of recognition, especially as the petrographical character of the rock species is subject to many modifications, and varies in different localities. For this reason there are many equivalents or representatives. The principal species occur in the following manner:

First, rauhkalk (rough limestone), which, when in normal position, rests on the zechstein. It derives this well-deserved name from the roughness of its exterior. Its rocks are generally full of cavities, and, in some places, contain large caves. Such are the Liebensteiner in Thuringia, the Schwartzfelder and the Steinkirche on the southern border of the Hartz. The rough limestone is sometimes represented by foetid and magnesian limestones, which are apt to incline to magnesian and foetid marls; the drusy cavities are sometimes clothed with rhombohedrons of magnesian spar. The colors vary from grey to white, and its cleavage is not regular. In the caves occurring in this rock tertiary deposits are found, containing bones cemented by stalagmite. Fossil remains are limited to single beds.

Next to the rough limestone comes the asche, an earthy foetid marl of ash-grey color, much darker when wet than dry, and non-fossiliferous.

Then comes the foetid limestone, which is extensively distributed in the compact form, and is found in thick beds; the shelly, oolitic, spathic, and breccious varieties are restricted to small districts. Zechstein and foetid limestone are closely allied, especially when the latter is in large masses. The bitumen which is diffused in foetid limestone is often concentrated in cavities as asphaltum. It contains few fossils; the forms are principally molluscan.

These principal features of the upper division of the copper slate are generally accompanied by loam exhibiting concretionary masses and traversed by fibrous gypsum, spathic and brown iron-stone, gypsum and karstenite, and rock salt. The gypsum and karstenite are of great purity, and stand in such connexion as to permit the assumption that the one has arisen from the other. Their chemical composition teaches us that karstenite needs only to acquire a certain quantity of water to become gypsum. This explains the fact that pieces of karstenite are inclosed by a crust of gypsum, having absorbed enough water from the atmosphere for the purpose. In mining gypsum we frequently come to a nucleus of karstenite. A considerable increase of volume takes place in this combination with water, and thus by its irresistible expansive action shatters entire mountains. On this account gypseous masses, when of large extent, have a greatly riven aspect. The rough jagged surface is quite characteristic of gypsum, this being produced by the dissolving action of water (one part being soluble in four hundred of water) upon the softer parts of the rock. B The compact portions remain behind and cause the roughness. The fissures which arise by the increase in volume of the karstenite, collect large quantities of water, which also exerts its destructive influence on the inclosing rock. Cavernous excavations are thus gradually formed, which may increase so much in time as that the incumbent covering of gypsum, not finding sufficient support, may fall in, causing sink-holes, which are sometimes filled with a saline water. This upper group of the copper slate formation often contains powerful springs, and is extensively diffused in England, in the Hartz, in Thuringia and Saxony, in North America, and various other places.

Among the geological equivalents may be enumerated the so called Frankenbergen formation, where limestone, slate clay, loam, sandstone, &c., rest on the transition slate and contain peculiar vegetable remains, presenting a distant resemblance to ears of grain, for which they were long mistaken. The copper sand ore formation of the west side of the Ural, constitutes another equivalent.

Fossils of the Copper Slate Formation. The fossils of this formation are rare and not well known. The vegetable remains are composed of a few Fucoids, Lycopodiaceæ, stems of not well determined monocotyledons and dicotyledons, Coniferæ: Cupressites ulmanni (the Frankenbergen grain ears), &c.; the animals of a few corals, as Escharites retiformis; Radiata, as Encrinites ramosus; shells, as Productus aculeatus (pl. 38, fig. 1), Delthyris alata, and species of Mytilus. The Vertebrata consist of fishes and reptiles; trilobites are entirely wanting, and are apparently replaced by Crustacea of a Limuliform character. Remains of fishes are numerous, and teeth of Acrodus larva (pl. 38, fig. 2), are characteristic of the zechstein. Reptiles first occur in the copper slate. The single genus known as belonging to this period, is found in the Mansfield copper slate, where its bones occur with fish remains. It is the Protero saurus, characterized by its long thin cylindrical teeth implanted in separate sockets. It forms the transition from the Lacertidæ to the crocodiles.

Pl. 46, fig. 10, exhibits an ideal section of the copper slate formation. Immediately on the carboniferous sandstone (a), lies the red sandstone (1), against which rests the white red sandstone (2). Then come copper slate (3), zechstein (4), a dolomitic rock (5), asche (6), old floetz gypsum with fœtid limestone (7), and marl beds (8). The whole is covered by the variegated sandstone (b).

Rock Salt Formation (Trias. Terrain salifere. Group triasique). The rock salt formation marks the commencement of the secondary formation of Elie de Beaumont, and immediately follows the copper slate. The principal rock species are sandstones, limestones, and marls, so arranged that the sandstones occupy the upper and lower portions, including the limestones in the middle, both species being combined by marly forms. Gypsum, karstenite, and rock salt are subordinate members, the latter of which, from its extensive distribution and intrinsic importance, has given name to the formation. Rock stilt is generally accompanied by gypsum and karstenite.

The only metallic minerals of importance are galena, electric calamine, and hvdrated oxyde of iron. Fossils occur in immense accumulations of individuals, although genera are few: they characterize the single groups and series of beds so perfectly, that no other formation can be compared to the rock salt in this respect: organic remains are, therefore, of especial importance for this formation. Three groups of the rock salt may be distinguished, sufficiently entitled to separation.

a. Variegated Sandstone Group. This is formed by sandstones of mostly red or reddish brown color, accompanied by clay and marl masses. Subordinate masses of the variegated sandstone are : quartz rock, clay quartz, limestone, sometimes oolite, gypsum, karstenite, and rock salt. Anions the fossils are vegetable remains of a terrestrial character. This group separates into three subdivisions; the first of which, the Vosges sandstone, is of rarest occurrence.

The Vosges sandstone is sometimes argillaceous, sometimes quartzose, sometimes hard, sometimes soft, either fine or coarse grained, and in single cases inclined more or less to quartz rock. The color is generally red, and the beds sometimes exhibit a thickness of 1000 to 1200 feet. It is mostly distinctly laminated, lying more or less horizontally, and free from subordinate beds and from fossils. It occupies the highest part of the Vosges and of the Schwarzwald.

The middle division, that of the variegated sandstone, does not exhibit, this uniformity : the sandstones are sometimes argillaceous, sometimes marly, and of different degrees of hardness, with the most diversified coloration; red predominates. Mica, chlorite, and talc, not seldom lie parallel to the planes of cleavage, as also dendrites of black oxyde of manganese. Calcareous and brown spar are often found crystallized in drusy cavities, these being not seldom found with a red barytes. The stratification is very complete, sometimes finely laminated, this being produced by mica, chlorite, or talc; it is also at times very thick, with double rectangular secondary cleavage, which, when in large beds, causes a tendency to a columnar structure. Quartz sandstone, whose strata are sometimes divided into cubes by the secondary cleavage, is limited to single layers.

Fossils occur only in particular beds, and are principally constituted by plants, bearing most resemblance to the coniferae of the torrid zone. Thus we have Albertia, with oval truncate leaves, inclosing the branch in horizontal series: A. elliptica (pl. 38, fig. 3^a). Voltzia comes very near to the Araucariece, and constituted the greater portion of the coniferous vegetation of the variegated sandstone period. Their leaves are needle-shaped and of different forms, so that on the same branch we may see short scale-like leaves alternating with long needles. The cones are covered with woody flaps, which stand at a considerable distance apart. Voltzia heterophylla is generally found in the form represented in pl. 38, fig. 3^b, more rarely in a combination of fruit-terminal and middle branches, as in fig. 4. Æthophyllum speciosum (fig. 5) is another allied form.

The upper division of the variegated sandstone, or that of the red marl, contains clays, marls, and sandstones, as the chief masses. Subordinated are quartz, granular and brittle quartz rock, this often covered with pseudomorphous crystals from rock salt; also limestone, oolite, gypsum, karstenite, rock salt, and celestine. The stratification is decided. The marls and clays, among which slate clay, clay marl, and marl clay belong, are of a reddish-brown color. Fossils occur but seldom.

Prominent mountain forms do not appear in the group of variegated sandstones; they form uniform ridges with undulating outline. The valleys generally run parallel to the secondary cleavages, and consequently cut each other at right angles. In deep valley intersections the walls are beset with picturesque rocks, frequently cleft, as near Kreuznach (pl. 49, fig. 9). In Sicily the variegated sandstone presents spacious caves (pl. 52. fig. 2). A sandy soil is produced by its weathering, well adapted to the growth of the oak and the pine.

This group is extensively distributed. It occurs of great extent in England, where it is known as new red sandstone; in Germany it is found in the Spessart, Odenwald, on the Rhone, in the Black Forest, in the Jura Chain, and on the west side of the Alps; also in France, Poland, United States, &c.

b. Muschelkalk Group. White sandstones predominated in the last group, limestones of various degrees of purity do the same here; they form the principal masses, and are accompanied by ferruginous brown limestone, fœtid lime, magnesian lime, clay sand marls, gypsum, karstenite, and rock salt. The purest limestones are generally met with in the middle of the group, which, receiving an addition of clay, becomes approximated to marly lime. Numerous individuals of few species constitute the fossils. The subdivisions are distinguishable, well defined by their palaeontological character.

The lower subdivision is indicated by marly limestones, not of a thick, but of an undulating and contorted stratification. These limestones sometimes alternate with bituminous and sandy limestone, tripoli, marly limestone, cellular limestone, &c. These masses generally appear in the lower portion of the subdivision, gypsum, karstenite, and rock salt occupying the higher Magnesian limestone and dolomite are also found, and at times in immense beds. The former is sometimes much decomposed; the carbonate of iron to which it owes its blue color passes by oxydation into hydrated oxyde of iron, which penetrates the rock and colors it yellow, while the hydrated oxyde of manganese, resulting from the carbonate of manganese, is separated in black or dark-brown dendrites. Immense beds of these limestones are often entirely free from fossils; single layers are nevertheless characterized by Buccinum gregarium, Dentalium læve, Terebratula vulgaris (pl. 38, fig. 10), and Myophoria vulgaris (fig. 9); metallic minerals are calamine, galena, and brown iron-stone.

The middle subdivision is characterized by purer limestones, of light or dark color, which are often colored reddish in weathering by the decomposition of carbonate of iron. They form immense beds, which appear to be almost entirely composed of shells, the principal material of which has been furnished by Terebratula vulgaris and Encrinites liliiformis. The stem-joints of the latter, shown in fig. 7, are entirely converted into calcareous spar, and the axis of these pieces coincides with the axis of the rhombohedrons, after which the former is cleavable. The heads of such Encrinites (fig. 6) are but rarely found, having generally been separated by destructive external influences.

The upper subdivision contains impure marly limestones of earthy, somewhat plane fracture, having a great tendency to the formation of spheroids, and separated by clay or marl masses. Single beds consist of magnesian limestone, dolomite, and ferruginous brown limestone. The fossils here met with are particularly Ceratites (Ammonites) nodosus (fig. 11). Terebratula vulgaris (fig. 10), Myophoria vulgaris (fig. 9), Avicula socialis, Lima (Plagiostoma) striata, Nautilus bidorsatus, Pecten lævigatus (fig. 8), Encrinites liliiformis (fig. 6), together with teeth and bones of Saurians and fishes. These fossils occur in a somewhat singular manner: they do not lie, as in the middle division, sown indiscriminately in the strata, nor in single strips in the beds, as in the lower, but more on the faces of separation so as to lie half in the limestone, half in the clay slate, which separate the limestone strata.

The muschelkalk is very distinctly stratified, but traversed by less regular cleavages, which sometimes widen into caves. Like the variegated sandstone, it mostly forms flat troughs bounded by gently curved saddle formations. Higher ridges have generally rectilineal contours with rooflike slopes. The weathering of the muschelkalk consists of a mechanical division, and contributes little to the formation of a soil: the subordinate clay masses are of more account in this respect. Springs are rarely found at high levels, more at low; they sometimes contain a proportion of sail when connected with deposits of rock salt. The upper division is not abundant, while the middle and lower are widely diffused. The muschelkalk is entirely wanting in England; on the other hand, it occurs in extraordinary development in Germany.

c. Keuper. (Marnes irisées; Red marls.) This group exhibits a considerable resemblance to the variegated sandstones, especially to the upper division. The principal rock species are clays, marls, and sandstones of various colors. Associated with these are quartz rock, ferruginous brown limestone, clay quartz, and many others; subordinate are gypsum, karstenite, rock salt, and coal. Where the group is complete three divisions may be established. The lower, that of the loamy coal and of rock salt, consists principally of slate clay, loam, and a highly fossiliferous sandstone (equisetum sandstone). The sandstone is of inconsiderable compactness, of an oil-green color running into grey, of thin or thick stratification, and frequently mixed with scales of mica. Among the fossils it contains, are species of equisetum, ferns, mollusca, fish, and reptiles. The clays also are tolerably rich in organic remains, especially in plants and shells. Among the latter Posidonia minuta is characteristic of the lower division; remains of fish and reptiles are found in marl clay and clay marl. These principal masses are frequently accompanied by ferruginous brown limestone, dolomite, and cement stone, and contain loam coal, in which a good deal of pyrites is disseminated: gypsum, karstenite, and rock salt are subordinate masses. The middle division, that of the variegated marls and gypsum, is principally composed oi clay and clay marl. The clay occurs in the form of shale, marl clay, and loam, frequently containing nodules of pyrites and argillaceous carbonate of iron. The clay and lime marl are worthy of note on account of the minerals they contain : among these are iron pyrites, lying scattered in the most beautiful crystals, calcareous spar, quartz, verdigris. and mountain blue : remains of fish and reptiles with the coprolites (petrified excrement) of the latter, characterize the fossil fauna. Accompanying masses are clay quartz, quartz rock, and dolomite : subordinate are karstenite and gypsum.

Sandstones prevail in the upper division, both fine-grained clay sandstones and quartzose. The argillaceous sandstone is of various colors of grey, red. and violet, producing the most diversified markings by their combinations. It contains vegetable remains, on which account it has been called rush sandstone.

The quartzose sandstone of yellow bluish or ferruginous color is occasionally dotted with white feldspathic particles, and sometimes includes pieces of silicified wood. Another sandstone with an argillaceous, calcareous, or marly cement, is of very coarse grain, giving to it the appearance of a conglomerate: it is this which has been named arcose by Brogniart. A clay, marl clay, or slate clay often occupies the rank of a principal member, although it must be included among the subordinate: it also contains the same Posidonia minuta which characterizes the lower division.

The Keuper is generally well stratified. The dolomite and magnesian limestone have a conspicuous secondary cleavage, often giving rise to the formation of caves. The thickness of this group amounts to about 1200 feet; its mountains may vary much in appearance according as one or the other rock species predominates. They are generally spherically convex, with irregular valleys and deep ravines; the protruding rocks have much similarity to those of the variegated sandstones. Ore veins have not as yet been found in the Keuper. The soil resulting from the weathering of the marls is of great fertility, owing to the amount of lime. Springs are not. abundant. The Keuper is found in England, Germany, Lower Saxony, Thiirincria. Swabia, the Jura; also in France, Alsace, &c.

Pl. 46, fig. 11, exhibits a section of the rock salt formation as it occurs in Würtemberg. The strata of the Vosges sandstone are indicated by a and 1, and those of the incumbent sandstone by h and 2. Then follows the muschelkalk, c, with the lower 3, the middle 4, and the upper division 5; upon these rests the Keuper, d, with its three subdivisions, 6, 7, and 8: the whole is covered by the lias.

Fossils of the Rock Salt Formation. The fossils characteristic of the individual groups and subdivisions have already been mentioned; it remains now to notice some of rare occurrence, worthy of remark on account of their palaeontological significance.

The fishes peculiar to the muschelkalk belong to the Hybodontes, a family of Plagiostomes, which enter here and pass off the stage in the chalk. They had bony spines in the dorsal fins, which are frequently well preserved. These ichthyodorulites have decided longitudinal grooves and two rows of strong serrations: Hybodus tenuis (pl. 40, fig. 4).

The teeth of the Hybodontes have a central larger lobe accompanied on each side by smaller decreasing ones, where covered by enamel they exhibit longitudinal grooves, the roots being broad and porous. The genus Placodus is peculiar, to the muschelkalk, in which only teeth and a few bones have been found. This genus is characterized by small, obtuse, conical intermaxillary teeth, and a vomer, with broad, much depressed dental plates. Pl. 40, fig. 5, represents an entire upper jaw with teeth and vomerine plates of Placodus andriani, found in the muschelkalk near Bamberg. Other remains are of Saurichthys mougeoti, &c. Rhomboidal scales of ganoid fishes, and especially Gyrolepis, are found in the muschelkalk: G. alberti, fig. 7^a.

The family of Labyrinthodonts, exhibiting relations to both Batrachia and crocodiles, is one of exceeding interest to the zoologist. They possessed a rough, depressed skull, with long conical teeth implanted in distinct sockets, and some of the anterior developed into formidable tusks. The exterior of the tooth is longitudinally furrowed, and a transverse microscopical section exhibits the most complicated foldings of dental tissue. A somewhat similar structure of less complexity is found in Ichthyosaurus, and some of the recent species of Lepidosteus. Fig. 8, pl. 40, represents the skull of Mastodonsaurus jaegeri, a labyrinthodont found in the keuper: fig. 9^a, is a detached tooth, fig. 9^b a transverse section of the same.

Tracks of birds and of other less decided vertebrata have been found in the new red sandstone of Connecticut (pl. 41, fig. 32). Upwards of 70 species of such ichnites have been established by Hitchcock. Some of these tracks are over 15 inches long, and 4 to 6 feet apart, indicating a size of enormous dimensions. A discovery of bones of birds in this formation has been recently announced.

Somewhat similar tracks of a different character have been found at Hildburghausen. They were sunk in a clay interposed between the strata of the variegated sandstone, the sandstone itself exhibiting the cast of the track (pl. 41, figs. 31^a, 31^b). They are batrachoid in their character, and were produced in great probability by Labyrinthodonts. The imaginary animal which produced these tracks was formerly known as the Chirotherium. Some fossils characteristic of the English saliferous system, which belong in this place, are Producta horrida (pl. 42, fig. 32); Retepora virgulacea (fig. 33); Terebratula globulina (fig. 34); Terebratula (fig. 35); Pecten radialis (fig. 36); Avicula gryphæoides (fig. 37); Axinus obscurus (fig. 38); Retepora fiustracea (fig. 39), and a fish, Palæothrissum macrocephalum (fig. 40).

Oolitic or Jura Formation. The Jura includes all strata between the rock salt or new red sandstone and the cretaceous system. The principal rock species are an oolitic limestone, clays and marls of tolerably uniform color, and a light-colored sandstone. Dolomite occurs in large masses as a secondary species. Fossil remains, especially animal, are very abundant, both terrestrial and fluviatile. Stone coal occurs in various parts, as also carbonate and hydrated oxyde of iron. Three groups may be distinguished.

a. The Lias (Calcaire à gryphites arquees, Marnes bleues inferieures. Terrain liasique). The principal species are clays and marls with gryphital limestone; the clays and marls in the form of shales, loams, clay marls, sandy marls, and calcareous marl shales, these mostly penetrated by carbonaceous particles, and inclosing nodules of sphærosiderite. In the Alps the slate clay is transformed into clay slate and calcareous clay slate.

The limestones are more or less pure, often containing iron pyrites and grains of earthy chlorite, foetid limestone, marly limestone, and sandy limestone.

Among the accompanying masses are sandstones of various colors and grain, which have much similarity to those of the keuper. Subordinate masses are gypsum, karstenite, rock salt, carbonaceous strata, anthracite, graphite, bituminous shale, drawing slate, and various iron-stones.

The sandstone, as also an oolitic marly red iron-stone, contains many fossils, of which Gryphæa cymbium and arcuata are most characteristic and important. The thickness of the group varies from that of a few feet to whole mountain masses. Ore veins are of rare occurrence and slight importance. A few sulphur and saline springs are occasionally met with.

This group is distributed in England, Germany, France, and Spain.

b. Jura Limestone. This is greatly developed in England, and there includes all strata lying between the Lias and the so-called Purbeck limestone. Oolite is a limestone composed of rounded spheroidal grains of various size, somewhat similar in character to a sandstone, and probably produced in the same way. Clays and marls accompany it, and separate the various lime strata. Subordinate masses are sandstones, gypsum, karstenite, rock salt, and carbonaceous masses. This group is divisible into three principal divisions.

The Lower Oolite. This is bounded inferiorly by the lias, superiorly by the Oxford clay, and embraces marly, sandy, compact, or oolitic limestones, and also true oolite, whose beds alternate with clays and marls. The limestones are generally light-colored, turning to ferruginous in exposure, this being caused by the presence of carbonate of iron. Bitumen causes a grey color. In England this division includes conspicuous beds of fuller’s-earth. The sandstones are conglomeratic, calcareous, marly, and ferruginous, with veins of fibrous carbonate of lime and arragonite; some are finely granular and quartzose, or passing into argillaceous quartz. Argillaceous sphaerosiderite and oolitic marls are subordinate species.

The thickness of the oolite of the Jura amounts to from 1000 to 3000 feet. In England, where the formation is highly developed, the following succession of strata occurs. Lowermost of all is the inferior oolite, separated from the great or Bath oolite by an immense bed of clay, exhibiting the character of fuller’s-earth (Terre à foulon). This great oolite is a partly compact oolitic, partly coarsely granular limestone, containing entire beds of corals. Between the great oolite and the fuller’s-earth there is, in the vicinity of Stonesfield, a bed consisting of marly sandstones and loose sand, with many concretions. This is the so-called Stonesfield slate, interesting from its containing the first remains of fossil mammalia. Next to the great oolite comes a stratum of marly clay, becoming sandy above, the Bradford clay, of a blue color, upon which rests the Forest marble, a limestone full of shells. On the Forest marble lies a thin stratum of slaty, coarsely granular limestone, the Corn-brash. Belemnites giganteus and canaliculatus, Ammonites Macrocephalus, &c., are characteristic fossils.

The middle formation, which embraces the Oxford clay and the coral-rag, contains purer compact limestone of white or ochre yellow color, calcareous slate or lithographic stone; oolitoid limestone, which lies intermediate between compact and oolitic, and often entirely filled with fossils; marble of various colors; marl and marl lime, of darker colors, owing to the presence of carbonaceous matter; dolomite and sandy limestone.

Subordinated are iron-stone in rounded great or small grains, gypsum, karstenite, rock salt, and coal of poor quality.

Immediately on the upper layers of the English inferior oolite there lies a stratum consisting of calcareous concretions cemented by marl, and bearing the name of the Kelloway rocks. Upon these lies a blue clay, the Oxford clay, containing thin lime and marl beds, and calcareous concretions. Next comes the calcareous grit, a calcareous loose sandstone. This is succeeded by the coral-rag, and this by the pisolitic lime, an oolitic limestone with grains and nodules of iron-stone.

The fossils characteristic of this group are Avicula pectiniformis, the corals of the coral-rag, Astræa helianthoides, Melanin striata, &c.

The upper formation [Kimmeridge clay and Portland oolite] contains purer limestones, like oolite, marly and sandy limestone, the latter often accompanied by clayey, sandy, and marly masses, often colored green by chlorite; also dolomite and fine grains of iron-stone.

In England the clay (Kimmeridge clay) lies under the limestone (Portland stone), in other places the former is replaced by sandy deposits. This Portland stone or Portland oolite contains species of Nerinea and Pterocera.

c. Wealden Group. This embraces the Purbeck marble, Hastings sand, and Weald clay, placed by some geologists in the cretaceous system. The accompanying strata are marls, slate clay, bituminous shales, marl clay, clay marl sandstone, iron sand, quartz rock, clay quartz, fœtid limestone, shelly conglomerate, and argillaceous iron-stone: these contain remains of fluviatile animals. Beds of stone coal sometimes in considerable thickness are occasionally met with. In England the group attains a thickness of between 900 and 1000 feet.

The Purbeck strata occupy the lowest position, and consist of limestones which alternate with slate clay. This limestone appears to consist almost entirely of the shells of Paludina and Cypris, evidently indicating a fluviatile origin. Between these strata are found remains of reptiles and especially of Chelonia. The Hastings sand lies above the Purbeck beds, and consists principally of a quartzose iron sand alternating with sandy clays and marls. Here also are found beds of iron-stone, stone coal, and numerous remains of extinct colossal reptiles.

The Weald clay overlies the Hastings sand, and contains strata of a bluish potter’s-clay, alternating with thin layers of a limestone filled with fossils that are very similar to those of the Purbeck marble.

Pl. 46, fig. 12, exhibits a section of the oolitic strata as it occurs in England.

The entire formation rests on the strata of the keuper (red marl) a; immediately on this lies the lias, b, which supports the true Jura limestone with the Oxford, c, and Portland, d, strata. The fresh water formation (Wealden) is shown in fig. 17 of the same plate.

In fig. 12, 1 indicates the lower lias strata, 2 the lias or gryphite limestone, and 3 the upper lias shale. Then follow the strata, 4, 5, 6, belonging to the lower oolite: after these the fuller’s-earth, 7; the Stonesfield slate, 8; great oolite, 9; Bradford clay, 10; Forest marble, 11; Corn-brash, 12; the Kelloway rocks, 13; the Oxford clay, 14; Calcareous grit, 15; Coral-rag, 16; Oxford oolite, 17; Kimmeridge clay, 18; Portland stone, 19. In fig. 17, 1 indicates the Purbeck marble; 2 the Hastings sand; and 3 the Weald clay.

The Jura formation in France forms the figure 8, the southern ring being completely closed. In the centre of the ring are elevated the granite masses, and the trachyte of Auvergne, about which the Jurassic members lie like a cloak. The northern ring incloses the Paris tertiary basin, forming a trough in which the latter is deposited. It is entirely crossed by an artificial canal. The lias contracts considerably, but occupies a greater extent on the western borders of the Vosges. It commences to the northwest of Luxemberg (pl. 44, fig. 6, and pl. 46, fig. 16), and passing by this place grazes Metz and Nancy, bends to the eastward at Dijon, and ends near Besançon. Over it lie the strata of the Jura proper, whose western border passes by Rheims, Troyes, and Auxerre, and almost reaches Lyons.

The Swiss Jura occupies a curve extending from SchafFhausen to below Geneva. It there forms high rock-walls furrowed by deep valleys of elevation, more abundant in the northern than in the southern portion. These valleys generally permit the older masses to emerge from under the newer. The newer strata form high lips with steep declivities, as shown in a valley of the French Jura (pl. 46, fig. 13).

The structure of these valleys may be explained by a cross-section of the valley of Bärschwyl in the Solothurn Jura (pl. 46, fig. 14). The bottom of the valley is formed by the gypsum bed of the keuper (6), towards which the keuper strata slope on both sides. Parallel to these are newer and newer strata, as the lias 4, the lower oolite 3, the Oxford marl 2, the Portland and coral lime I. These limestones, which are little affected by the decomposing influences of the atmosphere, form the precipitous lips of the valley.

The Swiss Jura forms an entire system of strata curves separated by such valleys of elevation. The latter appear parallel for small extents, but in their general direction they radiate from a point not far from Basle. The deeper the fissure, the older is the rock which forms the bottom of the valley, and the more rugged the appearance of the whole. Pl. 46, fig. 15, is a section of a portion of the Swiss Jura. The Portland stone and coral-rag are indicated by 1; 2 represents the Oxford clay; 3 the lower oolite; 4 the lias; and 5 the muschelkalk. The chain of the Weiss-stein, A, sinks its valleys only to the Oxford clay; the valleys of the Hauenstein, B, reach to the lias, as also do those of the Passwang, C. In Mont Terrible they extend down to the muschelkalk, which is elevated in the middle of the valley, D. The lips (a) formed by Portland stone and coral-rag represent the Hosefluh (a), and form a valley at the bottom of which lies Barschwyl (b). Schonthal (c) lies on the lias of the valley of the Hauenstein. The same lias extends under the Jura lime, cropping out first at Passwang and finally in the valley slope of Mont Terrible. The Renken (e) on the one side corresponds to the Rehhag (d) on the other.

The German Jura is a continuation of the Swiss : it begins at Schaffhausen, and extends through Franken into the vicinity of Bamberg and Baireuth (pl. 46, fig. 16). It describes a great arc, whose radius falls far in the interior of Germany. The strata of the Jurassic rocks fall in the same direction with this radius. The German Jura is divisible into three classes: the black, which consists of lias, and borders the entire series; the brown, whose strata correspond to the Jura proper, or the inferior oolite; and the white, whose masses are formed by the strata which lie over the coral-rag.

In the Franconian Jura, all the coral reefs, which compose a great proportion of the limestone masses, are converted into dolomite, having there a thickness of several hundred feet. In this transformation most of the organic remains are so much affected as to be scarcely appreciable, except in certain hollow spaces filled with a loose and finely-divided limestone, called mountain milk. The whole dolomite series is traversed by extensive fissures, from which numerous caves have arisen, celebrated for the bones imbedded in their tertiary contents. Among these caves are those of Streitberg, Muggendorf, and Gailenreuth. The Solnhofen slate, or lithographic stone, is an important member of the Franconian Jura. This is a very fine-grained limestone, of a yellowish color, and contains many fossils in an extraordinary degree of preservation. It overlies the coral-rag. The Alpine Jura exhibits a very highly complicated structure, its masses being so much modified by abnormal rocks as to render it a matter of exceeding great difficulty to draw a comparison between the strata as they occur here and in other localities.

Fossils of the Jura. The fossils of the entire Jura formation exhibit the most interesting and varied character. Fucoids occur in great number, of which, however, only one species is sufficiently well preserved to be noteworthy. This is Baliostichus ornatus (pl. 38, fig. 12), an unjointed sea weed, with branching sporangiæ, and with the surface divided into lozenge-shaped areas, arranged in spiral rows. It occurs in great beauty in the Solnhofen limestone slate. Conspicuous among the Cycadese, a form intermediate between that of the ferns and that of the Coniferee, we have the Zamiæ, as Zamia pectiniformis (fig. 13), in the Stonesfield slate.

The Cycadites, or Mantelliæ, are known by their almost globular stem, covered with lozenge-shaped leaf scars, broader than high, and disposed in spiral rows. Cycadites (Mantellia) megalophyllus (fig. 14) is found in the limestone of the Isle of Portland. Mammillaria desnoyersi, a species of an ambiguous family, is represented in fig. 15.

The coral polyps, which existed in great number in the transition rocks, but disappeared entirely in the entire trias period, again make their appearance in great profusion. The Astrææ, which also occurred in the transition, here play an important part. The most abundant species is Astrcea helianthoides. Labophyllia semisulcata (pl. 38, fig. 16) is the most important representative of its family. Two genera of pedunculated echinoderms or Crinoidea are conspicuous: Apiocrinites and Pentacrinites. The former genus, possessing a very large pelvis, is exhibited only in pieces of the stem, and occasionally the pelvis without arms: Apiocrinites mespiliformis (figs. 17 and 18). An interesting species of Pentacrinites, P. subangularis, is shown in figs. 19 and 20. These have a pentagonal column, upon which arms, variously divided and subdivided, are supported on a very small pelvis; they are peculiar to the lias, while the Apiocrinites are found in the coral-rag.

The Echini, or sea urchins, are conspicuous in the Jura formation. These have a more or less spherical shape, and are covered with calcareous plates with tubercles, upon which are jointed spines of various degrees of development. These may be conical or club-shaped, and may vary much in size. The shell is divided into regular patterns by the pores through which the animal extended its ambulacra or organs of motion. The large oral and anal apertures have different positions in the different families The Cidarites have the anal and oral apertures diametrically opposite to each other, and occupying respectively the centres of the vertex and base. The shell is furnished with large warts, on which are set large club-shaped spines, which, however, are generally broken off and dispersed. We find Cidaris (Hemicidaris) crenularis (pl. 38, figs. 21^a and 21^b) in the coral-rag, together with species of Cidaris blumenbachii (fig. 22). The zones on which the ambulacra stand generally run to a point. This, however, is not the case in Dysaster; here the rays unite in two points at no great distance from each other. The mouth of Dysaster lies anteriorly and below, while the anus is situated in the posterior border: D. capistratus (fig. 23), from the Oxford clay. The genus Clypeus is characterized by a rounded form, a mouth on the inferior surface, a lateral anus situated in a furrow above the mouth, and by the convergence of the ambulacral areas to a point in the vertex. Clypeus hugi (fig. 24) is found in the restricted Jura group. The genus Diadema, of which D. seriate (fig. 25) is found in the lias, is also of spheroidal form, and has ambulacral areas disposed in pairs, which run very regularly to the upper part. Two series of tubercles stand between the ambulacral arese, all appearing to have borne spines.

A few species of the genus Spirifer recur in the lias only to disappear from the fossiliferous series; S. walcotii (fig. 26) is met with most frequently in gryphital limestone. In the Jurassic rocks, Terebratulæ, in great number, appear to replace the Spirifers; thus Terebratula numismalis (fig. 27) occurs in the lias, T. globata in the inferior Jura, and T. impressa (fig. 28), as also T. thurmanni, in the Oxford clay.

Of Monomyaria, Ostrea (oysters) here make their first appearance. They form entire banks, as at the present time. The genus Ostrea has a toothless hinge, through which passes a cavity containing a ligament, with deep muscular impressions. Ostrea marshii (fig. 29) occurs abundantly in the Oxford clay, and O. deltoidea (fig. 30) in the Kimmeridge beds.

The Gryphææ are closely allied to the oysters, and are distinguished by the greater curvature and spiral twist of the beak of the larger shell. Two species are found in the lias, Gryphæa arcuata (fig. 31) and G. cymbium. G. dilatata (fig. 32) is met with in the Oxford clay, and G. virgula (fig. 33) in the Kimmeridge marl.

Plicatula is another genus allied to Ostrea. The shell is regularly plicated, and the beaks are not projecting; they are found in the lias: P. spinosa (fig. 34).

Of the Pectens, Pecten lens (fig. 35) is found in the lower oolite, P. disciformis (fig. 36) in the middle oolite, and P. personatus (fig. 37) in the lias.

The genus Perna differs essentially from the preceding in shape, in the long hinge, and in the extensive emargination in the anterior portion of the shell: Perna mytiloides (pl. 38, fig. 38).

The thick-shelled Trigonice have considerable resemblance to the Myophoriæ already referred to under the muschelkalk. They are more or less triangular, and have long, laterally compressed and furrowed cardinal teeth, of a V shape. Trigonia navis (fig. 39) characterizes the upper lias, and T. clavellata (fig. 40) the Oxford marl.

Pholadomya has a thin shell, open on both sides, with opposed beaks, but no teeth. P. exaltata (fig. 41) is peculiar to the Oxford clay.

Diceras possesses a very thick shell, running out into sub-spirally twisted beaks, and a hinge whose ridges exhibit some resemblance to a human ear: D. arietina (fig. 42).

Astarte has nearly circular valves shutting close together, and two cardinal teeth. It fills entire beds of the coral-rag, known as the Astarte limestone: A. elegans (fig. 43).

The Nuculæ, shells belonging to the family Arcaceæ, are extensively distributed in the Jurassic strata. They are small, regular shells, with four toothed hinges: Nucula hammeri (fig. 44, a and b). The genus Pinna is an elongated equivalve shell, whose beaks end in a point, and whose hinge margin is toothless. P. hartmanni (fig. 45) is found in the lower lias.

Pterocera oceani (fig. 46) is peculiar to the Portland limestone. This genus possesses a thick shell and a short axis. The oral aperture is narrow, and runs out above into a long canal. The external lip is expanded into a digitated wing. The Pleurotomaria have a thick, conically spiral shell, and a narrow quadrangular or rounded aperture, with a deep incision in the external margin, which distinguishes it from Trochus: P. conoidea (fig. 47) from the lower oolite.

Nerinea, a gasteropod genus, peculiar, excepting in one species, to the Jura, has a long conical, often cylindrical, spiral shell with very thick walls, and having highly characteristic internal folds. Certain species occur in great numbers of individuals, as N. suprajurensis (fig. 48), one turn of which is exposed in longitudinal section. N. mosæ, (fig. 49), and N. godhallii (fig. 50); fig. 51 is a longitudinal section of the latter. The most conspicuous Ammonites are Ammonites bucklandii (fig. 52) in the lias; A. catena (fig. 53), also in the lias, and A. striatulas (fig. 54) in the lower oolite.

There are a few species of the Nautilus family, as Nautilus lineatus (fig. 55), in the lower oolite. Here, as also in the muschelkalk, we find the beaks of cephalopods, known as Rhyncholites, or Conchorhynchs. These Rhyncholites exhibit a striking similarity to the mandibles of parrots or of Cheloniæ. Pl. 38, fig. 56, is a lateral view of one of these Rhyncholites.

The fossil known as Belemnites, belonged, in all probability, to a cephalopod, and, like the so-called ossa sepice, was an internal framework inclosed by the softer parts of the animal. They are generally conical bodies of various shapes, mostly of a crystalline texture, the crystals radiating from the longitudinal axis of the Belemnite (fig. 58, c). They run out below into a more or less acute point, and at the upper part exhibit a conical excavation. The ink bag of the Belemnite has been found in this cavity in a state of preservation sufficient to admit of the use of the contents in drawing the fossil itself. The internal structure of the cavity may sometimes be ascertained in the upper portion: in it was inserted an alveolus or phragmocone, with a chambered shell and a sipho quite like that of Orthoceratites (fig. 61 and fig. 58, b). A rarely preserved horny plate was connected with the posterior face of the alveolus (figs. 57 and 58, a).

Belemnites pazillosus (fig. 59, a) occurring in single strata of the lias in countless numbers, is readily distinguished by the channelled apex, shown in cross-section by fig. 59, b. B. giganteus (fig. 60) is of immense size, sometimes over one foot in length: it characterizes the lower oolite. B. hastatus (fig. 61) has a hastate cone, and is found in the Oxford marl.

The above-mentioned view of the morphological character of the Belemnites does not, however, explain the import of the chambered shell and the sipho. A more careful investigation of allied structures, both recent and fossil, renders it very probable that the animal itself lived in these chambers like Nautilus and Ammonites, a view which the occurrence of the sipho goes very far to substantiate. The shell of the camerated portion fs very thin and exceedingly fragile, for which reason it is inclosed by a thicker, more solid portion, as in Nautilus. This protecting cover is the conical body or rostrum so often met with in a petrified state, and, in all probability, has been secreted from a mantle. The animal, probably, inhabited the upper chamber, as in the Orthoceratites, Ammonites, and Nautili; its mantle was probably analogous to that of the recent nautilus. This view also explains how it is that the solid portion is composed of a succession of vertical layers, each one corresponding to a chamber. When the animal formed a new cell, this had to be enveloped by an additional external protecting cover, which, of course, embraced the portion already existing. The greater the number of chambers in the phragmocone, the thicker and longer the solid portion, and the greater the number of layers in the latter.

The strata of Solnhofen, which inclose so large a number of palseontological treasures, also exhibit fossil insects, belonging especially to the family of the Libellulidæ (fig. 62). The characteristic features of these insects, as the antennæ, the masticatory apparatus, the legs, and the nervatures of the wings, are not sufficiently well preserved to permit us to compare them very closely with the existing members of this family. Many of them are of colossal size, even attaining a length of six or more inches.

The Jura strata reveal a new page of fossil ichthyological history. We here find the heterocercal fishes, or those with an unequally lobed tail, receding into the background, and the homocercal coming forward in increasing numbers. The essential difference between the two consists in the prolongation of the vertebral column along the upper edge of the cauda fin in the former, while in the latter, the extremity of the body occupies a position nearly symmetrical, with respect to the two lobes or halves of the tail.

The teeth of Strophodus, a genus of the Cestraciontes, are depressed, truncated on both sides, and elevated in the middle, without a central longitudinal fold. Their axis is somewhat twisted, and the surface sometimes striated or reticulated; the root is broad and porous. Pl. 38, fig. 63, represents a tooth of S. longidens. The genus Pycnodus is the most abundant of the Pycnodonts. These were short and high fishes, with a strong skeleton. The eyes lay very high above the rather wide mouth. The dorsal and anal fins were of considerable extent, reaching to the homocercal caudal: P. rhombus (fig. 64).

In the family of the Lepidoides, the genus Dapedium is distinguished by a short and flat body, small head, and diminutive mouth, provided with sharp curved teeth. The fins are short and weak, the ventral and dorsal nearly opposite. The thick rhomboidal scales were covered with enamel, and connected by processes. D. punctatum (fig. 65) and D. politum (pl. 41, fig. 11) occur in the lias. The present creation exhibits few representatives of these fish with angular connected ganoid scales, the chief representatives being the North American Lepidostei, of which some ten species are known to naturalists. Pl. 41, fig. 12^a, represents one of these species; fig. 12^b, a portion of its jaw.

The species of Megalurus and Aspidorhynchus are conspicuous among the Sauroids. The former (pl. 38, fig. 66) have large rounded caudal fins, high dorsal, and large pectoral fins. Their shape is compact and stout, the head short, with a moderately large mouth, provided with thick conical teeth. Aspidorhynchus (pl. 41, fig. 13) was a very long, narrow, and cylindrical fish, with a long upper jaw projecting far over the under, both being furnished with conical acute and unequal teeth; the scales are higher than long, the dorsal fins opposite to the anal, and both very near the large forked tail. Both Megalurus and Aspidorhynchus are found in the upper Jura strata, the latter also in the cretaceous. Pl. 41, figs. 14–23, represent teeth of certain ambiguous fishes.

The reptiles of the Jura belong especially to the Enaliosaurians, represented by the genus Ichthyosaurus and Pleslosaurus. The Enaliosaurians are principally characterized by the fish-like vertebras. These are flat at both ends, and conically concave (pl. 42, figs. 24 and 27), forming a long vertebral column by their union. The four feet of the animals are broad and flat, without either fingers or claws, being thus true paddles. The normal bones of the feet are subdivided much more than in recent forms. The sharp conical teeth stand in long grooves of the jaws, and each one inserted in a distinct socket, as in the crocodiles. The head also exhibits some resemblance to these latter animals.

The Ichthyosaurus (I. communis, pl. 41, fig. 26^a from the Lias) has been found of a length of 40 feet. The large head possesses a long acute snout, furnished with 120 to 160 conical grooved teeth (figs. 26, b and c), interlocking together on closing the jaws. The eyes are very large and circular, with a bony sclerotic, composed of several plates such as are now found only in birds and turtles. The vertebræ are numerous, those bearing ribs amounting to as many as 40. The short neck contains only from five to ten vertebræ. The ribs inclose the whole body, and are connected with a T-shaped sternum. The anterior extremities are more powerful than the posterior, both probably having been covered with angular plates of horn, while the body was naked. Like some recent fishes, the Ichthyosaurus possessed a spiral intestinal canal, which impressed the same character on the excrements. These are frequently found fossilized, and are known as coprolites. They contain teeth, scales, fins, and bones of fishes, in large number, which, together with the general structure of the animal itself, allow us to consider the Ichthyosaurus as highly destructive to the animals with which it was associated, and to fish especially.

The Plesiosaurus is distinguished from the Ichthyosaurus by the possession of a very long flexible neck, provided with a much smaller head. The paddles were also longer and the tail shorter: P. dolichodeirus (fig. 25^a). The teeth (fig. 25^b) were conical and finely furrowed: P. macrocephalus (pl. 40, fig. 10).

The Pterodactyles, or flying saurians, are among the most extraordinary forms, either recent or fossil, known to zoologists: Pterodactylus crassirostris (pl. 41, fig. 35). They had a large head with very broad orbits, and unjointed bony sclerotics. The broad jaws are provided with long subulate teeth, inserted in special sockets. The long strong neck is set on a short trunk, which ends posteriorly in a thin short tail. The humerus is short and thick, the fore-arm more than twice as long. Upon the carpus is set a hand with powerful claws, the external finger being very long and falcate. The hind feet were tolerably long, thin, and attached to a feeble pelvis. The hind and fore-feet were probably united by a membrane, as in the Cheiroptera or bats of the present day, admitting of feeble powers of flight. The principal difference in the structure of the wings of the pterodactyle and the bat lies in the fact, that while the former has but one finger greatly developed, the latter has four.

The first traces of Mammalia are found in the Stonesfield slate, and probably belonged to carnivorous Marsupialia, Several genera and species have been distinguished, as Phascolotherium buchlandii (pl. 38, fig. 67, lower jaw).

The Jurassic fresh water formations are in some places, as at Neufchatel, replaced by marine limestones and marls. Of the fossils peculiar to the Neocomien, some of the most interesting forms will now be mentioned.

Of Echinodermata, Holaster complanatus (Spatangus retusus, pl. 39. fig. 13). The Holasters are cordiform, and possess curved ambulacral zones in the vicinity of the generative apparatus. The mouth is placed anteriorly on the lower side in a depression, the anus being situated behind and more towards the upper face. Other fossils of interest are Trigonia caudata (fig. 19), Mytilus simplex (fig. 28), Turbo plicatilis (fig. 35). Pleurotomaria neocomensis. The chambered cephalopods are represented by Crioceras, a genus characterized by its free turns: C. duvalii (fig. 38); also Ammonites macilentus (fig. 40); Scaphites and Toxoceras distinguished from each other and from ammonites by the character of their rolling up: S. ivanii (fig. 42) and T. bituberculatus (fig. 41).

In surveying the fossils of the Jura we observe a great variety of forms, among which the Saurians stand pre-eminent. The central figure of pl. 37, after Buckland, illustrates the extraordinary character and probable rapacity of some of the animals characteristic of the lias. In this representation a indicates the Ichthyosaurus communis; b I. longirostris about to devour a Dapedium politum, e; c, a Plesiosaurus dolichodeirus; and d, two Pterodactyles fighting. At the bottom of the water are Pentacrinites, f, Mollusca, Crustacea, skeletons of various animals. Ammonites and Nautili sail about on the surface with outspread mantle. The shores are lined with Cycadites, Coniferæ, Zamiæ, &c.

Pl. 42, fig. 31, represents Gryphæa incurva; fig. 30, part of the jaw of a crocodile; fig. 29, Pholadomya murchinsonii; fig. 28, Ammonites walcotii; fig. 27, a dorsal vertebra of Ichthyosaurus communis; fig. 26, Clypeus clunicularis; fig. 25, Cidaris intermedia.

Cretaceous System. The petrographical character of the Cretaceous System is essentially different from that of the Jura. The chalk forms a highly characteristic feature, although it does not occur in all cases. In addition to chalk there are compact limestones, marl clays, sandstones, sand beds, and conglomerates, containing gypsum, karstenite, rock salt, iron-stone, and coal, as subordinate masses.

The cretaceous system exhibits different features in different localities, having reference not only to the petrographical character, but to the distribution of the fossils. Such deviations from the normal character in the latter respect are found in the Alps, the Carpathians, in Southern France, Spain, &c., which in all probability have been effected by climatic differences. Plants are not very numerous; the few that do exist belong both to land and marine forms; leaves of terrestrial dicotyledons frequently occur. Animal remains are found in great numbers, especially marine species, among which may be enumerated Corals, Sponges, Alcyonia. Siphonia, Echini, Crinoidea; more rarely shells, particularly Sphaerolites, Hippurites, Turrilites, and Ammonites, which here disappear from the stage of animal life. The reptiles have become more similar to the present forms. The cretaceous formation is divisible into two groups.

a. Greensand (Grès vert), subdivisible again into two sections, the quadersandstein and the chalk marl. The quadersandstein consists of sandstones of very loose texture, occurring in some localities as sand beds. They are sometimes argillaceous, calcareous, or marly, sometimes ferruginous, or cemented by chalcedony: the colors are white, grey, and red; the lighter appear to predominate. The grain of these sandstones is of various character, fine, coarse, or conglomeratic. The sandstones themselves are occasionally traversed by veins of quartz, which remain in the weathered rock as intersecting elevations, and contain tree stems and shells. The accompanying clay beds are marly, and of a bluish color.

The lower regions of this formation are generally ferruginous, while the upper are of a greenish color, owing to the presence of chlorite.

Subordinate masses are granular clay, iron-stone, blue when fresh, brown when weathered, sandy argillaceous sphaerosiderites occurring in nodules or their aggregations, stone coal, lignite, and bituminous wood.

The second formation, that of the chalk marl, consists of various clays and marls, with limestones. The marls occur as flame marl, chalk marl, and as marl clay, or clay marl.

The flame marl is sandy, coarsely earthy, and of various shades of grey and yellow, whose uniformity is interrupted by dark spots, cloudings, veins. &c. A slight tendency to green is produced by the presence of a little chlorite. The chalk marl exhibits various shades of color, but not the markings so peculiar in the preceding; it is generally white, green, grey, or yellowish. The variegated clay marl, and marl clays, often exhibit a great similarity to those of the rock salt formation, and contain nodules and entire beds of fire- stone.

The limestones, often marly, are white and grey, more rarely blue and greyish black; the purer varieties have a conchoidal brittle fracture, and are frequently traversed by veins of calcareous spar; they are sometimes exhibited as marble or oolitic limestone, and are accompanied by clay or clay marl.

Subordinate masses are an iron-stone which is frequently mixed with green earth, gypsum, karstenite, and rock salt, all, however, only occurring in the marl.

b. White Chalk Group. This, also, is divisible into two formations, the lower of which is of most frequent occurrence. It is in this that the true chalk exists. The white color often passes into grey, reddish, or yellow, and the hardness varies from that of the chalk of commerce to that of compact limestone. Fire-stones frequently occur in nodules lying parallel to the planes of stratification, or in entire beds produced by the aggregation of the former. It consists, in great measure, like the chalk itself, of infusorial skeletons, recognisable by a good microscope.

Chalk rock comes near to the chalk proper, and consists of a white silicious limestone. The silex is not unfrequently separated in the form of nodules. Here belongs also the flag limestone, a compact rock of brittle fracture, and sometimes mixed with sand. The accompanying chalk marls are chalk white, and pass on the one hand into chalk, on the other into chalk rock. Dolomite is very rare; clay and loam beds occur between strata of firmer texture.

The upper formation is more seldom met with, and consists of Saugkalk, chalk (in Petersberg. near Maestricht) and a granular saugkalk of ochre yellow color. In these rocks there also occur nodules of freestone and of hornstone. A great variety of fossils is met with, among others, Lacerta gigantea, and Pagurus faujasii.

Above these limestones lie fossiliferous, earthy, sandy marls, of white, grey, yellow, green, or brownish colors. Clay and loam beds colored by greensand or oxyde of iron, occur as subordinate masses; also, a marly sandstone mixed with grains of earthy chlorite, a calcareous sandstone with many granules of lime, a calcareo-silicious conglomerate with fragments of shells, and a marly limestone.

The cretaceous formation is developed most completely in England, and has there been investigated most fully. A section of the stratification is exhibited in pl. 46, fig. 17. Beneath lie the strata of the Jurassic fluviatile formation; reckoned by many geologists among the cretaceous: they include the strata, 1, 2, 3. Upon these rests the lower formation of the first group: first the lower greensand, 4, with the gault, 5 (the blue clay bed); then the upper green sand, 6, differing from the sand masses of the lower green sand by the presence of a much greater number of green particles. It contains many silicious and not very compact concretions called cherts. Next come the chalk marl, 7, the Grew-chalk limestones, 8, and the white chalk, 9.

The upper formation of the white chalk assumes quite a different character in the Pyrenees, in the Alps, and in the Apennines. Conglomeratic slaty sandstones, resembling grauwacke, mixed with mica, occur here. They are known by the name of Macigno in Italy, in Switzerland as Flysch and Vienna sandstone, and contain many vegetable remains, especially of Fucoids, for which reason they have been called fucoidal sandstones. Hippurites occur in the limestones, but not in the northern chalk rocks; in the southern they are, however, found.

In the Apennines, a limestone and slate mass underlies, and contains large numbers of Spatangus retusus. Upon this rests the hippurite limestone, characterized by Hippurites, Radiolites, &c. Then follows the nummulite sandstone entirely filled with Nummulites; and lastly, the fucoidal slate, Flysch or Vienna sandstone.

Recent investigations of the cretaceous formation in France have given rise to the following division of the strata:

On the neocomien formation lies the lower chalk, the terrain aptien, embraced by the upper strata of the latter, and separated from it by its palaeontological characters.

Upon this is the terrain albien, consisting of the lower greensand and the gault, characterized by Inoceramus concentricus and Trigonia aliformis.

Then the chloritic chalk or the terrain turonien. It includes the upper green sand, the limestones of the upper formations of the first group (the craie tuffeau) and the chalk marl, and is decidedly characterized by the presence of Hippurites and Baculites. The senonian strata (terrain senonien) close the series, being composed of the true white chalk of both formations.

The stratification of the individual members of the cretaceous formation is much diversified : in the chalk rock it is very intricate, while in the quadersandstein it is exceedingly regular; double rectangular cleavage traverses it in such a manner as to produce cubiform blocks. The thickness of the cretaceous often exceeds 1000 feet. It sometimes forms whole mountains, whose external appearance is affected greatly by the particular member which is present. When the softer varieties predominate, they possess a gently rounded exterior; the chalk rock inclines to the formation of a spherical surface, and the quadersandstone to that of picturesque rocks. The chalk itself forms high cliffs, especially on the coasts.

The soil produced by the weathering of the quadersandstone is poor and sandy; that resulting from the marl very warm, on account of the amount of lime; for this reason it is well adapted to the growth of the vine. The springs are inconsiderable in number, and feeble in character; some, however, are exceptions in being quite copious: a few are saline.

The cretaceous system is extensively distributed; it is found in Denmark, England, France, Belgium, Germany, as in Mecklenberg, Lower and Upper Saxony, Westphalia, Bohemia, Franconia, and Silesia; it likewise occurs in the chain of the Alps and Jura, in the Pyrenees, in Spain. Portugal, the Apennines, Sicily, Greece, Hungary, Galicia, Poland, Russia; in Asia, on Mount Lebanon; in Northern and Southern Africa. The cretaceous system of North America differs in many features from that of Europe. True chalk is entirely wanting, the series being represented by greensand, marls, and a shelly limestone often of great compactness. It occurs in New Jersey, Maryland, Virginia, North and South Carolina, Georgia, Alabama, Arkansas, and various other regions.

In Germany, the cretaceous extends along the northern sea coast, and from Westphalia towards the east; it is very similar in character to the French system.

The lower strata are formed by the Hils clays (bluish clay with hard calcareous nodules), which are probably the equivalents of the upper part of the Neocomien formation; upon these rest sandstones, of more or less thin stratification, and of different colors of brown and red, with no great compactness, even running at times into quite a loose sand bed: these appear to correspond to the lower greensand. The strata of the gault are not well recognised in North Germany. The beds corresponding to the upper greensand are known in Westphalia as very similar to those in England and France; they are, nevertheless, principally replaced by flammen marl. Upon these lies the chalk marl, whose hard, marly, grey limestone, with alternating layers of clay, closes the highly fossiliferous series of the freestone chalk which occurs in such complete development in northern Germany on the Island of Rügen.

The lower chalk is developed in quite a peculiar manner in Saxony: it is there represented by masses of a fine-grained white, grey, or yellowish-brown quaderstein, whose regular fissures, cutting each other at right angles, form the delightful valleys of the Meissner uplands, or the Saxony Switzerland. Between the sandstone masses there passes a layer of limestone, readily splitting up into plates, known as the planerkalk, and appearing to correspond to the gault. The subjacent quadersandstone must in this case be considered as the equivalent of the lower greensand, and that above it as the upper greensand.

Fossils of the Cretaceous System. The chalk is very rich in fossils; among polyps, a prominent form is Hallirhoa costata (pl. 39, figs. 1 and 2), a spongeoid hard body, with a large aperture in the upper pedunculated and often lobed expansion.

The infusoria play an important part in the chalk, forming entire strata. Here belong the Rhizopoda (Foraminifera, Polythalamia), whose almost microscopic calcareous test was at an earlier period looked upon as the shell of a minute cephalopod, to which it has an unmistakable resemblance The shell, which contained a series of minute apertures for the passage of the organs of motion, is divided into chambers, which do not communicate with each other, each one inhabited by a distinct animal. This fact, while it negatives the cephalopod character, renders it probable that the shell formed a minute polypidom, inhabited by animals of a very low organization. The whole of the true chalk appears to have been formed from such shells. We need not be astonished at such abundance of infusorial shields when we reflect that one animal whose calcareous or silicious test may weigh \(\frac{1}{10000}\)th of a grain, is capable of so multiplying itself in thirty days, as that the sum of the resulting tests or shields shall weigh over 65,000,000,000 lbs., and be capable of covering a surface nearly fifteen square miles to a depth of two feet, with a density equal to that of water. The Rhizopods are divisible into various groups, according to the various position and character of the individual chambers. The Monostegia are shells with a single chamber; the Stichostegia have the chambers placed one above the other in a single straight or curved line; the Helicostegia, with chambers placed along an axis forming a spiral volute; the Entomostegia, with the chambers placed along two axes alternating with each other and rolled up into a spiral; the Enallostegia, with the chambers alternating along two or three axes, and not rolled up spirally: and the Agathistegia, or milliolites, in which the chambers are disposed spirally round an axis, each one occupying a semi-circumference.

Dentalina, which belongs to the Stichostegia, has a somewhat curved conical shell, consisting of spherical chambers, the latter often elongated. The single cells are separated from each other by no very deep contractions: Dentalina sulcata (pl. 39, fig. 3).

Textularia, of the order Enallostegia, has a conical and regular shell, with the round or wedge-shaped chambers arranged along two contiguous axes: T. aciculata (fig. 4).

The Helicostegia separate into two groups, according as the chambers are rolled up in a plane or in a turret. Bulimina belongs to the latter: B. obliqua (fig. 5). Between these and those whose turns lie in one plane, like the nautilus, stand the Rotalina, whose obliquely rolled columella is very short: R. voltziana (fig. 6). The Cristellaria exhibit the greatest resemblance to the nautilus, being a perfect miniature of the latter: C. rotulata (pl. 39, fig. 7). As Lituites is only a modified nautilus form, so Lituola may be considered as such with regard to Cristellaria. They are cristellaria whose cells suddenly lose the winding character, and run out in a straight direction: L. nautiloidea (fig. 8). The flat compressed shell of Flabellina is at first wound up very regularly, and afterwards expands in a foliated manner. The partition walls are at first simply curved, and afterwards interrupted: F. rugosa (fig. 9).

The infusoria hitherto considered are those found in the white chalk. In other calcareous masses of the cretaceous system allied forms occur, as in the nummulite limestone which occurs in the Pyrenees. The nummulites fill the above-mentioned series in countless numbers, and would be highly characteristic did they not also occur in the Hippurite limestone. The internal structure of the nummulite is often beautifully revealed on breaking open a piece of nummulite limestone, in which case it will most frequently happen that one or more of the shells will be split in two, as they are of sufficient size (sometimes an inch in diameter) to permit this fracture (fig. 10). A nummulite consists of an aggregation of spirally wound chambers, separated from each other by obliquely disposed, almost vertical partitions. Fig. 11 is a cross-section.

Certain Echini are very characteristic of single beds of the cretaceous. In the white chalk Galerites is distinguished in this respect: G. albo-galerus (fig. 12). This genus belongs to the Clypeasters, known by their nearly conical shape, and by the occurrence of the ten-cornered mouth in the middle of the base, with the anus in the posterior border. The five ambulacral zones run directly from the vertex to the mouth. The plates are well defined, and possess feeble tubercles, upon which stand slightly developed spines.

The Hippurites, or Rudistes, come near to the Brachiopoda, and are highly inequivalved bivalves. The lower shell, attached either below or at the side, is much the larger, and is closed by a smaller operculoid valve, without hinge or ligament. The figure is very irregular, as they formed beds like oysters, and of course were obliged to accommodate themselves to the spaces left vacant by the contiguous individuals. The shells of the Hippurites are very thick, yet, nevertheless, so often destroyed that only stony casts, in the form of two cones, placed base to base, remained behind, and were known at an earlier period under the name of Birostrites or Jodamia. Considerable uncertainty was for a long time felt as to the true place of these animals in the scale, and the divisions in the lower part of the shell gave rise to the erroneous idea that they belonged among the cephalopods. This supposition is now, however, completely refuted, and the study of the closely allied Crania enables us to place it with a considerable degree of certainty among or near the brachiopods.

The Rudistes separate into several genera, particularly into the true Hippurites and the Sphærulites. The former have a very long conical lower shell, with acute base and several longitudinal furrows. The much smaller upper shell is very flat and operculoid, and this contributes to the formation of a simple conical stone nucleus: H. organisans (pl. 39. fig. 14) and H. bioculata (fig. 15).

The lower shell of Sphærulites is smaller and the upper larger than in the preceding. It therefore appears as two unequal cones, placed base to base, with ridged and often foliated surface: S. ventricosa [Radiolites turbinata] (fig. 16).

Among the true Brachiopoda may be mentioned Crania, whose small, almost circular shells, are attached by their lower portion. The lower shell is flat, and has a process, on whose sides are two deep muscular impressions, which also exist on the upper free conical valve; the process and valve impressions are sometimes wanting. The border of the shell is provided with warty elevations. Fig. 17 represents the inner part of the upper shell; fig. 18, the same from below.

Trigonia aliformis and T. scabra (fig. 20), and Cardium production (fig. 21), represent their respective genera.

The Ostraceæ are quite different in form from that which we found to prevail in the Jura; the family is here represented by Exogyra, differing from the displaced Gryphæa by the laterally bent beaks: E. columba (fig. 22) and E. sinuata (fig. 23).

Inoceramus comes rather near to the oysters; they are inequivalve shells, of tolerably triangular form. The opposing beaks are strongly bent, and the hinge has a number of indentations: I. concentricus (fig. 24) from the greensand.

Spondylus with inequilateral, spiny shells, has two teeth in the hinge, and two strong muscular impressions: S. spinosus (fig. 25) from the white chalk.

Pectunculus, represented in the upper greensand by P. subconcentricus (fig. 26), is a genus of shells, equivalve, and closing tight, the curved hinge provided with teeth, separated from each other by deep intersections, the cardinal area covered with broken lines, and the border provided with fine teeth. Closely allied to these is the genus Nucula; fig. 27 represents a cast of N. pectinata from the lower greensand.

The species of Opis have two very thick tapering cordiform valves provided with very long beaks, and a complicated hinge with a large compressed tooth: O. elegans (pl. 39, figs. 29 and 30), from the upper greensand.

The genus Acteonella is a characteristic representative of the Gasteropoda in the cretaceous. The individual turns of the shell embrace each other in such a manner as that the aperture occupies the entire length. The aperture is very narrow, and is contracted still more above by three thick ridges. A. crassa (fig. 31) is peculiar to the chloritic chalk. Avellana is much more universally distributed than the preceding, and is characterized by its short and rotund shell with crescentic aperture, and three strong teeth on the inner margin, the outer border with small long transverse teeth: A. incrassata (fig. 32) from the gault.

Rostellaria has a subfusiform or turreted spiral shell, with the upper part of the aperture ending in a long tube, and the margin dilated into a wing, or digitated, the wing sometimes falcate towards the apex. The species occur from the upper Jura to the present epoch. A characteristic species for the chalk is shown in fig. 33: R. parkinsoni. Pterocera pelagi (fig. 34) is peculiar to the white chalk, Natica lyrata (fig. 36) to the chloritic chalk.

The Cephalopoda of the cretaceous system present many points of interest. The Nautilidæ occur with simple windings and simple smooth partitions. The Ammonitidæ, previously so remarkable for the fringed and varied attachment of the partitions to the main shell, assume a new character in approximating to the earlier simplicity of the preceding family. At the first appearance of the Nautilidæ, it will be remembered that the single chambers were combined in various ways, either in a linear direction, as in Orthoceratites, or the axis a little curved at the vertex, and then continued in a straight line (Phragmoceratites) or rolled up below (Lituites), and subsequently entirely rolled up in a single plane, as in the true Nautilus and Goniatites. The opposite condition of things prevails in the ammonite family. At first they occur as completely chambered shells, with the windings in the same plane and in contact with each other; in the cretaceous system, when about to disappear from the fossiliferous rocks, they begin to exhibit the original character of the Nautilidæ. The Crioceras of the neocomien come very near to the true Nautilus (see fossils of the Jura). Toxoceras and Scaphites of the same beds stand further removed, as also do the Hamites of the gault. The Baculites of the Ammonitidae correspond to the Orthoceratites of the Nautilidæ: in the former, the chambers with fringed or sinuated margins are superimposed along a straight axis. Pl. 39, fig. 43, represents Hamites attenuatus, and fig. 44, Baculites anceps, found in the middle chalks. Of the true Ammonites, A. varians (fig. 39) is found in the white chalk. The various forms of the Ammonitidæ just referred to, have had their turns all in the same plane. Turrilites has them in different planes, so called from being of a turreted form (T. costatus, fig. 45). This genus is distinguished from Helicoceras by having the turns in contact.

Belemnites mucronatus (pl. 42, fig. 22) is known by the deep emargination of the base.

The fishes of the cretaceous period exhibit a transition from the more ancient forms to those of the present day. Pl. 40, fig. 7^b, represents the quadrangular broad teeth of Ptychodus latissimus, hitherto only found in the white chalk. The ganoids become less abundant, and in their stead come cycloids and ctenoids. The scales of Beryx are represented in fig. 7^c.

A gigantic lacertan reptile is found in the upper cretaceous group of Maestricht, Mososaurus hoffmanni, as also some crocodilians; the cretaceous of North America, likewise, embraces species of Mososaurus. The Maestricht beds also contain teeth of Iguanodon mantelli (fig. 11^b). But few remains of birds occur, a partial skeleton is shown in fig. 12.

Other fossils, characteristic of the English cretaceous, are Pecten quinquecostatus (pl. 42, fig. 13); Apiocrinus ellipticus (fig. 14); Spongia cribrosa (fig. 15); Marsupites milleri (fig. 16); Inoceramus sulcatus (fig. 17); Trigonia alceformis (fig. 18); Cotillus brogniartii (fig. 19); Ammonites varians (fig. 20); Plagiostoma spinosum (fig. 21); Belemnites mucronatus (fig. 22); and Scaphites costatus (fig. 23).

Tertiary Middle Series

In ideal succession, the tertiary middle series lies immediately above the newest deposits of the secondary middle. This, however, does not always occur in nature, and although the tertiary beds are not found between the older rocks, they yet at times rest upon them, and even upon abnormal masses, by which they are not unfrequently pierced and overlaid. In the latter case, the abnormal must be the newer of the two; it is generally basalts that present themselves among the tertiary in this manner.

The thickness of the tertiary is sometimes very considerable, as, for instance, on the Righi, 6000 feet high; they also occur at considerable elevations, although much more abundant in older lower regions, where they fill troughs or basins of the older rocks, or extend along the sea coasts. A crystalline structure is not often found to exist in the rocks; and even sandstones and conglomerates are more rarely met with than loose sand and water washed beds. The clay occurring here is always amorphous, and limestones sometimes exhibit traces only of crystallization. Calcareous tufa, that loose lime deposit from calcareous water, is here found for the first time. Mineral species are not numerous: they generally consist of arsenical and iron pyrites, while hydrated oxydes of iron and manganese penetrate the rocks, and are sometimes found in separated deposits. The position of the stratification, generally indistinct, is mostly horizontal or basin-shaped, rarely upheaved, this only taking place in the vicinity of abnormal masses. Peat is found in beds of much economical importance.

The task of arranging and classifying tertiary deposits is rendered very difficult, by the fact that they vary so much in different localities; it therefore becomes necessary to have frequent reference to geognostical equivalence in comparing the tertiary of different regions. Special reference must be had to fossil remains, which, while distributed in great number, yet exhibit considerable local variations of form. It will be seen, that during this epoch of the world’s history, considerable climatic differences prevailed on the surface of the earth.

The dicotyledonal form of plants prevails in the tertiary, and, while polyps become rarer, mollusca increase so as to form entire beds. Belemnites and ammonites have entirely disappeared; and, on the other hand, insects, fishes, reptiles, and mammalia, with some birds, become very conspicuous. The reptiles assume more familiar forms, and the mammalia are represented by pachyderms, none belonging to recent genera; ruminantia come next; and last of all, carnivora.

These organic remains are generally in much better preservation than in the older formations, from not having been exposed so long to the tooth of time and the accompanying destructive influences.

The views of different geologists with regard to the classification of the tertiary masses vary very much. Some rest it upon the different number and character of the contained fossils, but the method is liable to many sources of error. The arrangement which we shall here adopt is that of Hausmann and Bronn.

Calcaire Grossier, or Coarse Limestone Formation. This formation, which embraces the so-called limestone as a conspicuous member, rests, when in normal situation, directly upon the newest cretaceous strata. The principal rock species are: various limestones, among them the pisolite lime, a ferruginous, coarse limestone, sometimes oolitic and traversed by streaks of clay; a purer, compact, often sandy limestone, which often passes into a true shell conglomerate, a limestone slate, and a silicious limestone (calcaire silicieux) often containing hornstone and chalcedony, and known as meulière de Paris, or French buhr stone.

Marls, among them a sandy, argillaceous, marly lime, and marl clay, sometimes assuming a slaty texture. These masses are generally grey, yellowish, or reddish in color, and bituminous. Adhesive slate is sometimes imbedded in the calcareous marl, as also freestone and some other silicious substances. A compact celestine sometimes occurs. Clay, as potter’s clay, marl clay and loam, of which some are important in the arts, as the Argile plastique and the London clay.

Sand and sandstones, the former predominating, and sometimes marly, sometimes argillaceous or ferruginous. The sandstones exist sometimes as argillaceous, sometimes as marly or ferruginous sandstone; in the latter case they often have a tubular, rough appearance.

Among the subordinated masses belong gypsum beds; among them the Paris bone gypsum. This is sometimes compact, sometimes sparry, and closely mixed with carbonate of lime. In the tertiary deposits gypsum again occurs in marl; also peat, and iron-stone.

This calcaire grossier or coarse limestone is highly developed in the Paris basin, and has there been carefully studied, especially by Cuvier and Broo-niart. The strata occur in the following order:

Beneath lies the pisolitic limestone (calcaire pisolitique), a marine formation, characterized by Corals, Echini, Dentalium, Serpula, Cytherea, Venus, Cardium, Area, Solen, Natica, Cerithium, Fusus, &c. Cerithium is found in great abundance.

Next comes a plastic clay (Argile plastique), whose purer lower bed is separated from the impure upper by a layer of sand. It contains both fresh water and marine shells, as Planorbis, Paludina, Melanopsis, Cyclas, and Ostrea. Also remains of Crocodiles and Chelonia, as the genus Emys.

Then follows a purely marine formation, the calcaire grossier proper, whose lower beds are of an arenaceous texture. Upon the limestone mass lies a sandstone of tolerable firmness, much used in Paris for building purposes; on this, again, rest beds of marl and firmer limestone. The lower strata of the calcaire grossier contain nummulites; the middle exhibits a vast number of fossils, the most abundant of which are: of plants—Equisetum brachyodon, Pinus defrancii, Confervites, Endogenites echinatus, Flabellaria parisiensis, Caulites, Potamophyllum multinervis: of vertebrata—Palæotherium, Lophiodon, and Chelonia: of shells—Milliolites, Cardium obliquum, Lucina saxorum, Ampullaria, Cerithium, Orbitolites plana, Cardita avicularia, Oddites elongata, Alveolites milium, Turritella imbricata, Calyptræa trochiformis, Pectunculus pulvinatus, Cytheræa nitidula and elegans. Turritella multisulcata, Ostrea Jlabellula, Natica epiglottina, Trochus agglutinans, Cerithium cornucopiæ, &c.

Upon the calcaire grossier rests a silicious lime (calcaire silicieux de St. Ouen), in the lower part of which fluviatile and marine shells are found intermixed, while in the upper, fluviatile alone are met with.

Then follows the marl with the bone gypsum, also fresh water formations, as they are filled with Cyclas, Paludina, Planorbis, &c. The bed attains a thickness of 170 feet, and, in addition to the fossils already mentioned, contains likewise fishes and mammalia; of the latter, Palæotherium, Anoplotherium, Adapis, Didelpnys, &c. There are also remains of birds, crocodiles, sea and fresh water turtles, &c.

The series is closed by a deposit of sand, sandstones, and marl, of marine origin, and containing Ostrea (O. flabellula especially), fishes, &c. In the sand there is found the so-called crystallized sandstone of Fontainebleau, which, however, in reality it is not. It consists of an aggregation of rhombohedrons like those of calcareous spar; in fact, these crystals are only carbonate of lime mixed up with sand. It is a little remarkable that the force of crystallization should have been great enough to overcome these impurities.

The Paris tertiary basin rests upon the cretaceous. Pl. 44, fig. 6, exhibits a map of it, in which its distribution may be more readily followed. Fig. 7 is a section of the same. The line a indicates the level of the sea, 1 the tertiary, 2 the cretaceous, and 3 the Jurassic strata.

The London tertiary basin exhibits certain features distinguishing it from that of Paris; while in the latter, limestone masses entered in considerable prominence, in the former, clays and marls predominate. The bone gypsum is entirely wanting. The masses occur in the following order:

Beneath lies a plastic clay very rich in fossils; upon it rests the London clay, a fat clay, with many marly concretions and shells, as well as remains of turtles and crocodiles; then follows the Bagshot sand, a sandy marl, with numerous marine fossils, and a non-fossiliferous sandstone. In the southern part of the English Bagshot sand, in the Isle of Wight, and on the coast of Hampshire, large beds of marine strata alternate with fresh water, consisting of greenish limestone, marls, and sand beds, in which are found remains of reptiles, Anoplotherium, and Palæotherium.

In Provence, in the calcaire grossier, there is found a bed of coal, intermediate between lignite and peat; it contains remains of various insects, especially of the Coleoptera. This formation is known in Germany, occurring here and there in single patches, as in Mecklenburg, near Kressenberg and Sondhofen in Bavaria, and in Mark Brandenburg; also, in Prance, England, Hungary, Southern Russia, Upper Italy, in North America, and the East Indies.

Molasse, or Upper Tertiary. Quite loose sandy, marly, or argillaceous masses have the preponderance. There are numerous mammalia in great variety, and of known forms. The principal rock species are:

Nagel-fluh, which passes into sandstone and marl.

Sand and sandstones, especially marly, argillaceous, calcareous, and ferruginous, frequently colored by chlorite and mixed with mica. They often contain concretions of lime and hydrated oxyde of iron, and pass into quartz-sandstone and quartz-grit.

Læss and loam. Loess is only a very fine well-washed loam, occurring over considerable tracts.

Clay, in the different varieties, as porcelain, potter’s, pipe-, marl-clay, &c. Not seldom it is bituminous and aluminous, and contains, as foreign admixtures, iron and arsenical pyrites, sulphur, gypsum, sphserosiderite, celestine, and a granular clay iron-stone.

Marl, as calcareous and argillaceous marl, which are often mixed with sand and mica. Shells occur in great number. The principal foreign minerals are sulphur, iron pyrites, arsenical pyrites, gypsum, and petroleum.

Limestones, which in general are very subordinate; they are met with as compact, slaty, loose, oolitic, marly, and breccious; as also marly lime, which is often bituminous. Likewise foetid limestone, silicious limestone, sandy limestone, and a calcareous conglomerate.

Among the true subordinate masses belong gypsum, often in the form of purest alabaster, rock salt, lignite, not unfrequently inclosing amber, mellite, humboldtine, and retinasphaltum. Iron and arsenical pyrites often occur, as also silicified wood; likewise a granular, argillaceous, or sandy iron-stone. Carbonate of manganese or rhodocrosite is occasionally met with.

The metalliferous sands of the molasse are of great importance, the metals being disseminated in the form of fine grains, as of platinum, gold, magnetic iron-stone, titanic iron, chrome iron-stone, tin ore, &c. These are obtained by stirring and washing the sands in the water, when the metallic matters fall to the bottom by reason of their greater specific gravity. Diamonds are sometimes obtained in a similar manner.

This formation is divisible into two groups:

a. Lower Group, or the Marl Formation. The principal mass consists of clay, sand, and marl, among which occur sandstones and fresh water limestones. Fossils exist in this formation, generally similar to those of the present day. There are numerous genera of Pachydermata, or thick-skinned mammalia. Beds of brown coal, of great extent and thickness, are accompanied by clay or sand, or, instead of the latter, by sandstone, converted into quartz grit in the neighborhood of abnormal masses. In these brown coal beds, and especially in the lower portions, upright stems of trees are met with. The brown coal experiences considerable modification in the vicinity of those abnormal masses, generally basalts, which penetrate them. The nearer to the latter, the greater the similarity to stone coal; and at the surface of contact the coal is changed into a lustrous coal, disposed in short columns perpendicular to the abnormal mass. These beds sometimes become inflamed by the oxydation of some of the included mineral substances, and thus exert an igneous action on the rocks with which they are in contact. In this manner the porcelain jasper is produced from clay masses. In the vicinity of the brown coal there sometimes occurs polishing slate, or tripoli, consisting entirely of the shields of infusoria. Leaves and fruits (Phyllites and Baccites), especially of Thuja, Juglans, Salix, Populus, Betula, and Acer, are found in the coal, but are specifically distinct from any of the present epoch. Remains of fishes and reptiles are also embraced in this group.

The region of Mayence furnishes an illustration of local variation in the marl group, a section of which is presented in pl. 46, fig. 18. Beneath lies a blue marl clay (1); next to this come sea sand and conglomerate, with numerous remains of Cetacea and Plagiostomes; then a brackish-water limestone, or one containing both marine and fluviatile shells, with Mytilus faujasii and Ceritfiium plicatulum (2–7); above the whole are sand and sandstone masses, in which lie imbedded numerous remains of terrestrial mammalia.

A curious formation is found at the foot of the Alps, not readily referable to any particular position; it seems rather to belong between the upper and the lower groups. The molasse there lies beneath, with marl and calcareous sandstones predominating; upon this is nagel-fluh of coarse grain, with subordinate beds of marls and sandstones. Then comes a shell sandstone, composed of true sandstone and nagel-fluh, embracing numerous fossil shells.

b. The Lower Group, or the sub-Apennine Formation. Sandstone is of inconsiderable extent, but marl and clay masses, as also pebbles and boulders, rarely combined into solid conglomerates, are abundant. The limestone is principally fresh-water, and in the form of calcareous tufa. Shells are numerous. Of mammalia are found deer, oxen, bears, hyenas, and mastodons; all, however, of extinct species.

Among the primary masses of the sub-Apennine formation belong marls of mostly dark colors, passing into sandstone and slate clay; they embrace celestine, iron pyrites, asphaltum, petroleum, &c.; of sandstones, calcareous, marly, argillaceous, and quartzose sandstones, in the form of pebbles and boulders, sometimes united into conglomerate. Gypsum is subordinate, including the alabaster of Volterra.

As a general thing the marls occupy the lower portion, the sand and pebble masses the upper regions. The marls and sandstones embrace vast numbers of shells, mostly in good preservation; also remains of mammalia, as elephants, rhinoceros, cetacea, &c.

This second group of the Molasse is well called the sub-Apennine group, as it borders the Apennines and forms its outskirts.

In this sub-Apennine formation are to be included the sand and pebble deposits on the south coast of Spain, containing single strata, entirely filled with oysters and pectens. The same strata are met with in Southern France and in England, in which latter country they are known as Norfolk and Suffolk Crag. Here likewise belong sea-sand beds found in patches in various parts of Germany, and also embracing shells. These deposits contain various marls, sandstones, and limestones, in which are subordinated beds of iron-stone and drift.

The thickness of these masses varies considerably; they sometimes form hills and even entire mountains. They not rarely are pierced and overlaid by basalts, which, in many cases, has been the cause of their preservation from the denuding action of the water currents. The occurring fossils are entirely local. The quartz grit sometimes contains leaves of trees and opalized wood. Some of the animal forms are Corals, Nummulites, Clypeaster, Nucleolites, Spatangus, Terebratula, Ostrea, Pecten, Pectunculus, Venus, Solen (as S. hausmanni), Turritella, fishes, &c.

The diluvium of Buckland belongs under this head. It consists of sand with subordinated clay and earth, sometimes consolidated into rocks of considerable firmness. The argillaceous portions are generally inferior, and upon them are spread out the sandy. There are also isolated sand hills, with various kinds of detritus, as also the drift accumulations of the north, which are of wide extent, reaching even into the river valley of the Elbe and Weser. These constitute the so-called erratic phenomena. Erratic boulders are often of considerable size, and are generally derived from more northern mountain regions. The petrographical character of the boulder sometimes enables us to decide with tolerable accuracy as to its native locality. In the south of Europe such blocks sometimes occur as the one shown in pl. 46, fig. 19, from forty to sixty feet in diameter, and found near Monthey in the Pays de Vaud. At this period masses of still more limited occurrence were formed, as a fresh water limestone, calcareous tufa, or older travertine, containing hornstone, jasper, and flint. In it are found Lymnæa, Planorbis, Paludina, Helix, Pupa, Cyclostoma, &c. Volcanic tufas and conglomerates are sometimes associated. Mammalia are represented by proboscidian pachyderms, oxen, and deer. To this same period belong the calcareous conglomerates and osseous breccias, often found elevated at a considerably high level on the southern coast of Spain; also, the calcaire mediterranien of Nizza, the clefts filled with shelly conglomerate, and the bone deposits of caverns. The latter are extensively distributed, and occur principally in cavities of limestone rocks, which have been shattered or fissured in some way or other, and the fissures excavated by the action of water or corrosive gases. At the bottom of the caverns there generally occur blocks and bones of various kinds, often cemented by a ferruginous mud and sand, the whole mass covered by stalagmite, stalactites depending from the top and sides. The origin of stalagmites and stalactites has already been explained. The bones are generally broken and crushed, especially the long bones of the extremities. Many in certain localities exhibit traces of carnivorous teeth, as of hyenas, wolves, &c. Some are rounded by the action of water. The cavities of the larger bones will frequently be found to contain fragments of bones belonging to smaller animals. Bone caves generally occur in series of hollows, connected by narrow passages.

Various theories have been propounded as to the manner in which these deposits have been produced, but no single one, nor indeed a combination of all, is sufficient to account for the phenomena which are sometimes presented. Some have been introduced, no doubt, by the agency of rapacious beasts which made dens of the caverns. Thus, in the celebrated cave of Kirkdale in England, unmistakable evidence of this is presented in the fact, that with the bones are associated, in vast quantities, the excrements of hyenas, and the bones themselves are broken and shattered in precisely the same manner as if they had been subjected to the action of hyenas of the present day. The association of water-worn sticks, pebbles, &c., with the bones, also shows that to the action of water may be ascribed a considerable share in the phenomena. Again, many caves are connected with sink-holes or katavothra, funnel-shaped depressions in limestone regions, into which water pours from a greater or less extent of country. Such pits being thickly overgrown with bushes, naturally afford a secure harbor for predaceous animals, which drag their victims into these localities for security. The accumulating and broken bones are carried down into the cavity at the bottom of the pit by the next heavy rain, and thus either dropped into the subjacent or associated caverns, or accumulated in the narrow galleries of the roof or sides. The richest deposits are frequently found in horizontal or inclined galleries or excavations in the roof of the cave, and under such circumstances as to preclude the possibility of an introduction through the mouth or main entrance. Such sink-holes may also seem to explain the introduction of certain foreign earth-beds and masses into the cave, as also in some measure the excavation of the cave itself.

Some of the most celebrated bone caves are the Baumann’s-cave and Biels-cave in the Hartz, the cavern of Gailenreuth (pl. 52, fig. 9, in section), and the Wirksworth cave in England (pl. 38, fig. 68, in vertical section). Among other remains, the complete skeleton of a rhinoceros was found in this cave. Its skull and horn are shown in pl. 40, figs. 14 and 15. Similar caves are found in other parts of England and Germany, in France, Russia, and in other portions of Europe. Of other parts of the world, Brazil is extraordinarily rich in such caverns. Dr. Lund has investigated nearly 200 of these, and obtained a large number of extinct species. Few bone caves have hitherto been found in North America, although in the abundance of caverns it is exceedingly probable that many are ossiferous. Remains have been found in the Mammoth cave of Kentucky, in a cave of Greenbrier county, Virginia, and in several caves of Cumberland county, Pennsylvania.

It will thus be seen, that our division of the tertiary after Hausmann and Bronn, is into the Calcaire grossier and the Molasse, with their individual deposits. The principal of the other systems of classification is that of Mr. Lyell, adopted by most English and American geologists. Supposing the number of fossil shells in the entire tertiary to be accurately ascertained, that series of strata in which three and a half to five per cent, of the species are identical with living forms, is called the eocene; a proportion of about eighteen per cent, of recent species constitutes the miocene; thirty-five to fifty, the older pliocene; and ninety to ninety-five, the newer pliocene. A classification of this character, based upon the proportion in which existing species occur, may and does answer an excellent purpose when all the fossil shells have been studied and ascertained; where this is not the case, any such arrangement must be liable to incessant modification.

Fossils of the Tertiary Period

The infusoria play a great part in this period of the world’s history as well as in the preceding, as immense beds are sometimes entirely composed of the remains of such animals. In the Paris calcaire grossier, beds are found made up of minute shells, known formerly as Milliolites. They are now divided into many genera. These microscopic shells seem to belong to Rhizopoda, whose turns were arranged in an imbricated manner about a longitudinal axis, so that each new turn partly or entirely covered the older.

In Bilocuhna (B. opposita, pl. 39, fig. 46), the turns lie opposite to each other, and embrace in such a manner, that only two such turns are visible. Triloculina exhibits three such turns: T. communis (figs. 47 and 48). Both are found in the calcaire grossier, as also Scutellæ, very flat echini, of discoid shape: Laganum tenuissimum (figs. 49 and 50). Of shells there are Voluta dubia (pl. 42, fig. 1), Dentalium striatum (fig. 2), Venericardia planicosta (fig. 3), Fusus bulbiformis (fig. 4), Emarginula reticulata (fig. 5), Turbo littoreus (fig. 6), Scalaria foliacea (fig. 7), Murex tubifer (fig. 8), Fusus contrarius (fig. 9), Cyprcæa avellana (fig. 10), Trochus agglutinans (fig. 11), and Pleurotoma exorta (fig. 12). An immense number of fossil fishes is found in a local marl slate of the calcaire grossier on Monte-Bolca in Verona. They are all of extinct marine species, belonging to the Percoids, Chaetodonts, Scomberoids, Clupeoids, Sparoids, and Aulostomes. The most peculiar fishes of the southern calcaire grossier are Acanthonemus filamentosus (pl. 40, fig. 1), Semiophorus velifer (fig. 2), and Aulostoma bolcense (fig. 3). The reptiles closely resemble those of the present epoch; among them are crocodiles, lizards, snakes, frogs, &c. One of the most interesting is Andrias sckeuchzeri, whose skeleton, as exhibited in one specimen, is shown in pl. 41. fig. 24. It is a well known fossil, but derives its celebrity principally from the fact that Scheuchzer described it as a fossil man under the name of homo diluvii testis. It belongs to the Urodelian Batrachians, of which it is the largest known representative, and stands intermediate between the existing Menopoma of North America, and the Megalobatrachus of Japan. In the fresh water formation are found many articulata, as Coleoptera, Crustacea, Arachnida, &c. (figs. 1–10. There are many genera and species of fossil mammalia. One of the most interesting forms is that of Dinotherium. Its true place in the zoological system is not well ascertained, some naturalists ranking it with the herbivorous cetacea, others among the mastodons. It formed one of the largest of all terrestrial mammalia; D. giganteum (pl. 41, fig. 29). The most gigantic of all ruminantia is exhibited in the Sivatherium (S. giganteum, pl. 40, fig. 13), whose remains have been found in the Himalayas. The head equalled in size that of the elephant, while the elongation of the nasal bones indicates the existence of a trunk or proboscis. On the forehead stood two short thick horns.

Palæotherium, a link connecting the rhinoceros and tapir, is an interesting form from the calcaire grossier. Several species have been distinguished, the largest equal in height to the horse, although rather stouter (P. magnum, pl. 40, fig. 18^a and 18^b). Anoplotherium was not far removed from the latter, whose remains, associated together, are found in the Paris calcaire grossier. It gives no indication of having had an elongated snout. Its formula of dentition is the same as in Palaeotherium, with this difference, that the teeth form a continuous series without any interruption, &c. A. gracile (pl. 41, fig. 27). They attained the size of an ass, had a long, thick tail, and were more slightly built than the Palæotheria.

The genus Rhinoceros is found only in the upper tertiary beds. Perfectly well preserved specimens have been found in the ice of Siberia, under circumstances similar to those already mentioned with respect to the mammoth or priscine elephant. Canines are wanting in the rhinoceros, and of incisors sometimes there are \(\frac{2}{2}\), sometimes none. There are several molars on each side of both jaws. Rhinocerus tichorhinus is of frequent occurrence (pl. 40, figs. 14 and 15).

Fossil elephants are very widely diffused, but most abundant in the high north, especially in Siberia: the ivory from this region of country enters largely into trade. Perfect specimens have been obtained from the ice-cliffs, covered with a woolly hair mixed with longer bristles. Their grinders are composed of vertical lamellae, of dentine, enamel, and cement; and there are but two teeth, sometimes only one, on each side of the jaw. A molar of Elephas primigenius, or mammoth, is represented in pl. 40, fig. 16, from the upper surface.

The genus Mastodon, now entirely extinct, exhibits close relations to the elephant, having the same general structure of frame, tusks, proboscis, &c., but differing in the molar teeth. These, to the number of one to four on each side of the jaw, exhibited two rows of mastoid or nipple-shaped protuberances of considerable size along the face of the tooth; these were sometimes united, so as to exhibit a series of transverse high ridges along the tooth. Some individuals possessed tusks of immense size. This genus is represented by several species, the existence of only one of which, on the continent of North America, has been satisfactorily ascertained. This species (Mastodon giganteus, pl. 40, fig. 19, head) is found in various localities, the most celebrated being Big-bone Lick in Kentucky. It has, however, been found in many other States of the Union. The most perfect specimens exist in collections in Cambridge and Boston, as also in Philadelphia, the British Museum, &c.

Armadilloid animals, which at present are only found living in South America, are represented by fossil forms in Europe. Some extinct species of very large size have also been found in the sands near Buenos Ayres, as Glyptodon clavipes, six feet long (pl. 40, fig. 11^a). This possessed an armor composed of hexagonal pieces; as also other anatomical peculiarities distinguishing it from its allies.

Megatherium, found in various parts of North and South America, is represented, perhaps, by but a single species, M. cuvieri. Pl. 40, fig. 20^a, is a figure of a skeleton sent to Madrid from Buenos Ayres. This animal was of a clumsy build, having a great similarity in the form of the skull to the sloth. It occupied a position in point of size between the elephant and the rhinoceros. It had neither incisor nor canine teeth, but 18 molars. Its mode of life must have been somewhat similar to that of the sloth, although probably not arboreal. It seems rather to have procured its food (twigs and leaves) by uprooting trees, which it was well capable of doing by means of its sharp claws, immense straight and thick broad tail, &c. Pl. 40, fig. 20^b, is a supposed restoration of the animal.

Mylodon was not unlike Megatherium in general character, and is represented by three species. A complete skeleton was found in the sands of the Rio de la Plata, not far from Buenos Ayres; it is about eleven feet long, and is preserved in the Museum of the London Royal College of Surgeons: Mylodon robustus (fig. 21). The other two species are M. darwini, from Brazil, and M. missouriense, from various parts of North America.

The diluvial Felidæ or cats, judging from their remains, must have been of terrific rapacity. The entire framework of many of these animals indicates a power entirely sufficient to compete with the gigantic forms by which they were surrounded. In strength of frame, if not in actual size, some of these exceeded the largest lions and tigers of the present day. Smilodon populator, from Brazil, is an extraordinary form, more nearly allied to the hyenas, however, than to the true cats (pl. 40, fig. 17). A scull of Hyæna spelæa is shown in pl. 41, fig. 33, and of Ursus spelæus in fig. 34. Fig. 28 represents a skeleton of the gigantic fossil Irish elk, Megaceros hibernicus. We may remark that the majority of remains from the European bone caves belonged to deer, bears, hyenas, &c.

The existence of fossil Quadrumana in the European tertiary, although at one time doubted, is now beyond any question. Pl. 40, fig. 22. represents the lower jaw of Pithecus antiquus, a species found both in Southern France and in England.

Pls. 39 and 41 contain representations of two animals prominent among the fossil Mammalia of North America. Pl. 41, fig. 30, represents a large specimen of Mastodon giganteus from Missouri, as mounted by Koch, and by him called Missourium theristocaulodon (or tetracaulodon). In mounting the skeleton the discoverer erroneously made the tusks turn too much outward. Their true position is as in the elephant of the present day. The original specimen was purchased by the British Museum, and reconstructed by Professor Owen.

Pl. 39, fig. 51, represents a skeleton of a fossil cetacean from the rotten limestone of Alabama, as incorrectly restored by its discoverer, Koch. It is the same as was exhibited in the United States and Europe as Hydrarchos harlani, or sillimanni, and erroneously supposed to be an Enaliosaurian of gigantic size, allied to Ichthyosaurus and Plesiosaurus. It is now well known to be one of the cetacean Mammalia, and bears the name of Basilosaurus, given to it by the first describer, Harlan. It has also received the names of Zeuglodon. Phocodon, Dorudon, and Squalodon. Several species are now known from the American tertiary, and similar remains occur in the eocene of France, south of Bordeaux. It must not be understood that the skeleton we represent was found in its present connexion, or even belonged to the same individual; it is such a restoration from different individuals as we are entitled to make when the proper caution has been observed. We have already referred, however, to the inaccuracy of our figure.

Figs. 58 and 59 represent fragments of the head; fig. 66 is an ideal restoration of the entire head; the other figures represent different portions, as ribs, vertebræ, phalanges, portions of the head, &c. The highly characteristic teeth are shown in figs. 60 and 61.

Top Series

The top series embrace the masses known as Alluvium, and which are even now in process of formation. The term includes both normal and abnormal masses, the former containing remains of animals and plants that still exist, even including man and his works of art. A portion of the alluvium belongs to the prehistoric period; the rest has been formed either before our own eyes or those of our ancestors. Alluvium is divided by Hausmann as follows:

Masses which have Experienced No Great Change of Position

Under this head belong:

a. Beds Formed under the Influence of the Sea, such as accumulations of shells with sand and gravel, which gradually unite into a solid shell conglomerate, and often lie at a not inconsiderable height above the present level of the sea.

b. Newest Marine Limestone, of Varying Degrees of Compactness and Solidity. It is generally of a light color, sometimes colored brown by oxyde of iron. It contains numerous remains of marine animals, very rarely human bones: pl. 41, fig. 36 shows a human skeleton from Guadaloupe.

c. Coral Reefs, which, partly destroyed, are converted into conglomerate, and are no longer inhabited. They frequently have an annular shape, and form the atolls or coral islands, of which so many occur in the Pacific ocean (pl. 49, fig. 2).

d. Newest Marine Sandstone, produced by the cementation of littoral sand by lime or oxyde of iron. Its colors are white, grey, or red; and the formation exists well developed in the straits between Italy and Sicily. It frequently includes remains of marine shells.

Formations Produced Under the Influence of Running or of Standing Water

a. Traventine, or Newer Calcareous Tufa. It either forms the bottom of pristine lakes or ponds, or is deposited in the vicinity of springs or waterfalls. This latter is the case in the cascade of Teverone near Tivoli (pl. 52, fig. 5). The traventine sometimes overlies peat, and is covered by loam; sometimes it lies on older masses, in which case the strata may occupy a rather high level. They are generally accompanied by oxydes of iron and manganese, and are sometimes bituminous. Fossils are very numerous in single portions, and generally of still living forms, as Helix, Planorbis, &c, among shells. Stems of grass, leaves, moss, &c., contribute not a little to the porosity of the rock. Bones of mammalia, as of deer, oxen, &c., with their tracks, are met with; as also the products of human industry.

b. Silieious Tufa, a deposit from hot silicious springs. It forms either conical hills on whose summit the spring is generally revealed, or else the filling up of cavities, as in the crater of the great Geyser of Iceland (pl. 44, fig. 17).

c. Soda and Salt, which are sometimes deposited on the edges of lakes.

d. Deposits of Borax (boracic acid).

e. Deposits of Alum and Magnesia.

f. Beds of oxyde of Iron, on the bottom of lakes.

Masses which have Arisen Directly from the Decomposition or Destruction of Rocks

a. Piles of loose blocks, occurring on the sides of mountains, and sometimes covered with soil, in which case they may give rise to the phenomena of land slides.

b. Gravel Beds, produced by the weathering of rocks. Thus we have granite, gravel, syenite-gravel, &c. These gravels are sometimes cemented anew, and produce the so-called regenerated granite or syenite, and granitic conglomerate.

c. Earthy Masses produced from the subjacent rocks, and occupying their original position.

d. Masses produced by the Decomposition of Plants, among which peat stands pre-eminent. We distinguish wood, leaf, and moss peat, according as one or other of these substances contributed principally to the formation of the peat bog. The deposits generally occur in depressions, yet sometimes in elevated places. Their origin presupposes a water-tight soil, such as is produced in particular by clay and granitic gravel. The beds vary in extent and thickness, the latter being greater in the middle than on the borders, as world naturally result from a deposit in a trough or basin.

Peat often includes mineral bodies, among which may be mentioned pyrites, gypsum, yellow and brown iron-stone, limonite, phosphate of iron, and retinasphaltum. The distinction is made into green and black moss, according as the moor is overgrown with vegetation or not; another distinction may be made into peat from marine and from fresh water plants.

e. Masses produced by Animal Agencies. Here belong the beds of silicious meal, which are really aggregations of infusorial shells, mixed with the pollen of pines, &c. Here also are to be ranged those deposits of guano occurring on the coast of Patagonia, Peru, &c.

Masses which have Experienced a Change of Original Situation

Here belong:

a. Glacier Walls, or Moraines, blocks of rock heaped up by the movement of glaciers.

b. Masses in River Beds, carried along and spread out at the mouth of the stream, so as to form a delta.

c. Masses Washed from the Banks of Rivers, and finally spread out on the bottom of the sea.

d. Dunes or Heaps of Sand, piled up on the shores of seas by the action of waves and storms, and carried landwards. They slope gently towards the sea, and fall away abruptly towards the land (pl. 44, fig. 8).

Common Earth

This constitutes the external crust of the upper series and the tillable soil. This is either rendered so by human industry, or is a purely natural product, as in the primitive forest, where it is produced by the fall and decomposition of vegetable matter. (Pl. 51, fig. 1, represents a primitive forest of Brazil.) The proportion of humus in soil is very variable, sometimes more and sometimes less. It plays an extensive part in respect to the nutrition of plants, both on account of its decomposition in carbonic acid and water, by the action of the oxygen of the atmosphere, and of its porosity, which facilitates a condensation, and even a chemical transformation of gases, ammonia in particular.

Springs and Artesian Wells

Before passing to the consideration of abnormal masses, it may be proper to premise a few general remarks respecting springs.

It is a well known circumstance that vapors constantly ascend from seas, lakes, streams, &c., which are condensed in the higher regions of the atmosphere, according to physical laws, and there forming clouds, are again precipitated to the earth in the form of rain, snow, hail, &c. It is the process of distillation on a large scale that provides the dry land with water, which presents itself either in the form of springs or subterranean currents. The masses with which we have become acquainted in our study of normal rocks, are, as we have seen, of a higher or lower degree of density, and are capable of taking up a less or a greater quantity of water. This water passes naturally from the higher to lower levels, and emerges at the latter in the form of springs, or else it continues subterraneously to neighboring lakes, seas, or other bodies of water. Many springs are exhibited in caverns or mines, as in the Dunold Mill Cave, near Kellet in Lancashire, where the walls are clothed with deposited limestone (pl. 53, fig. 2) The springs may be of various kinds of origin; thus a hole sunk near the bank of a river may lead to a stratum saturated by lateral absorption from the running water in the bed of the stream; they may be produced by the emergence of brooks and other streams, after disappearing in the earth; by lakes at high elevations; by the melting of snow and ice in glacier masses, from which the water emerges in a stream (pl. 49, fig. 5, the Rheinwald glacier, where the water emerges in several places); they may also arise when an inferior stratum in a series is water-tight, and the rain falling on the earth sinks to this stratum, and passes along its upper face until it meets with a suitable outlet, either natural or artificial. This latter kind is of especial interest, as permitting the construction of Artesian wells. An Artesian well can only exist when the water which is to supply it collects between basin-shaped strata. Pl. 48, fig. 2, illustrates the conditions necessary to the production of an Artesian well; the water, draining from a considerable elevation and extent of surface, sinks into basin-shaped strata, and there accumulates by coming between strata impervious to water. A pressure will thus be exerted upon any point of the inclosing walls, equal to that of a column of water, whose height is the vertical height of the most elevated portion of the layer of water above the point in question. If, then, the interspace, a, between two impervious strata be reached by means of a hole bored through the incumbent masses, the water may flow out through the hole, and be carried by hydrostatic pressure to a height b, equal to that of a. If a tube be inserted in the hole, the elevation of the ascending stream will be modified by the resistance of the air and the friction on the walls of the tube; thus the actual height of the water in the tube will be less than that which is theoretically possible.

On boring at a point, d, lying higher than the body of water, c, the water will only partially fill the tube, that is, to the level of c.

The boring of Artesian wells is attended with many difficulties, as it requires an accurate knowledge of the geognostical character of the country to make success anything more than problematical. And even if success be theoretically certain, unknown and local conditions may exist in the subjacent strata to render such success impossible. Boring instruments of different character are required for different kinds of rocks or deposits, and the peculiarities of the particular case may be such as to require a highly inventive genius to suggest new apparatus suitable to the emergency in question, when all the old appliances have failed. The principal kinds of boring tools are those intended to penetrate masses of slight consistence, as in fig. 11; those intended to elevate watery, muddy, or pasty masses from the bottom of the cavity, as in fig. 12, consisting of a cylinder provided with a valve, so that substances may enter, but cannot pass out again without assistance; finally, those intended to penetrate hard rocks, and for this purpose provided with sharp corners (figs. 6 and 7). These instruments are screwed to strong shafts or attached by iron pins, and set in vertical and rotary motion by various forms of machinery, this being effected in a specially contrived house or shed. Fig. 4 represents the interior of such a boring shed. The hole must be lined with tubing, to prevent a filling up by pieces of rocks, gravel, or other substance, which might slip in from the side. These tubes are adjusted in their place by means of the borer, 14. The instrument, 5, is employed to extract the tubes again, by screwing into them and thus elevating them from the cavity. It sometimes occurs, that the shafts to which the borers are attached, break off in the hole; in this case, the instrument, 9, is employed, which, being screwed around the upper end of the broken shaft, takes firm hold of it. The other borers, 8, 10, 13, and 1–30 of the boring shed are used in particular cases.

One of the most important and interesting Artesian wells ever constructed is that of Grenelle, near Paris, in which, for eight years, the operation was continued, and which was sunk to a depth of 1961 feet below the ground, or 1696 below the level of the sea, thus nearly four times as deep as the elevation of the cathedral- of Strasburg. (See fig. 3.) According to the report of the engineer, M. Mulot, who directed the boring, the geological peculiarities of the strata passed through, were as follows:

1. Alluvial masses to the depth of twenty-seven feet.
2. Argile plastique, with muschelkalk, quartzose and argillaceous sand, variegated clay, &c, to the depth of about 173 feet.
3. White chalk, with beds of dolomite and silex, to the depth of 910 feet.
4. Compact grey chalk, with silex here and there in the upper portion, extending to a depth of 1480 feet.
5. Chalky Glauconia strata to the depth of 1666 feet.
6. The gault, with iron pyrites, phosphate of lime, and fossil remains in the upper portion; green and white sand occurring in the lower and middle strata.

Although some geologists have ascribed to subterranean lakes the origin of the water emerging from Artesian wells, there are many circumstances that conclusively prove that, in most cases at least, these waters are entirely of immediate atmospheric origin. An Artesian well at Tours, on the Loire, brought up remains of plants and shells from the calcaire grossier, the origin of which could be pronounced upon with all confidence. The plants were of such a character and appearance as that they could not have been in the water for more than three or four months. Other Artesian wells, as those at Elbeuf, Bochum, &c, have occasionally thrown up eels, groundlings, and other animals.

Pl. 48, fig. 1 is intended to furnish a coup d’oeil of the normal masses. The abnormal masses have been considered as the oldest, for the sake of separating them from the normal.

• A. 17. Abnormal masses, strata 1–4
• B. Normal masses, viz.:
• 16–11. Primary or bottom series, strata 5–16
• 10. Transition slate system, strata 17, 18
• 9, 8. Carboniferous system, strata 19–22
• r–o. Kupferschiefer formation, strata 23–26
• n, m. Rock salt, or saliferous formation, strata 27, 28
• l–g. Jura formation, strata 29–33
• f–a. Cretaceous, strata 34–38
• 6–3. Tertiary masses, strata 39–61
• 2, 1. Upper series, strata a–e

Influence of Water upon Rocks

Water exerts a very great influence upon the masses composing the earth’s crust. Water descending from the clouds in the form of rain, naturally contains such substances as are floating in the atmosphere; among these are carbonic acid, traces of ammonia, and, under certain circumstances, very slight traces of sulphuric acid. The inorganic particles originally contained by water are deposited or separated from it in its evaporation. When the water again descends, it not only retains its original inherent property of dissolving and disorganizing portions of rock, but will be found to have derived additional power in this respect from the carbonic acid. Water by itself, or chemically pure, is incapable of dissolving carbonate of lime, but after obtaining carbonic acid from the atmosphere, and still more from the humous particles of the soil, it can effect this solution in considerable quantity. The portions of lime taken up are generally deposited in fissures, veins, caves, druses, &c, in the form of calcareous spar, stalactites, &c. The chemical effect of the carbonic acid is to form a soluble bicarbonate of lime with the original carbonate of the limestone. Similar influences may be exerted upon other masses besides limestone, so that a gradual destruction of all rocks is taking place with greater or less rapidity. The greatest mountains will, then, in time, be completely dissolved, like sugar in water. Rain water, while thus decomposing rocks chemically, and disintegrating them mechanically, acts upon them afresh in transporting them towards the ocean or still lakes, where they are again deposited in the form of strata. The natural tendency of things, then, is to elevate the valleys and low regions, and depress the elevated, and so to reduce all to the same level, or to the regular spheroidal solid. Another mode in which the destruction of rocks is effected is by the force of waves and currents. The breakers of the sea, dashing with irresistible force upon the rock-bound shore, shatter the rocks, and breaking them into blocks of various size, spread them upon the bottom. Wherever, then, the coast is lined with rocks, these generally are fissured, cleft, or otherwise affected so as to be exhibited in every variety of form. Innumerable instances might be adduced. We shall only refer to the curious serpentine rocks on the coast of Cornwall, in the bay of Mullian, not far from Lizard Point (pl. 53, fig. 7), and the rock groups on the Faroe Islands (pl. 49, fig. 3).

The force of waves not rarely results in the production of caves, some of them of considerable dimensions. Among these may be mentioned Fingal’s cave on the Isle of Staffa, inclosed by the most beautifully symmetrical columns of basalt (pl. 52, fig. 6); the fresh-water cave (pl. 51, fig. 4), and Blackgang cave (fig. 5) on the Isle of Wight; and the peculiar arch of rock on Cape Parry, in the arctic regions (fig. 3). Similar formations occur in the case of fresh water streams and lakes.

Waterfalls, too, in particular cases, produce striking results. Thus the entire body of water in Lake Erie, in pouring into Lake Ontario, dashes over a precipice of about 160 feet in height. The rock wall over which the water pours is continually undermined by the impact of 670,000 tons of water in every minute falling from the top, and the upper portion crumbles gradually away, so that the falling mass constantly recedes in position. At some future day the recession may extend to Lake Erie, and the result may be the draining of the lake itself, or even of the entire lake series, thus adding nearly 72,930 square miles to the land surface; a cataclysm of no ordinary magnitude when, in addition to the above result, we consider the effect which must be produced by the impetuous bursting of all their barriers by the waters in the descent to the sea. Pl. 50, fig. 8, represents the Niagara Falls from the American side. Similar phenomena are presented by the Dal-Elf-Fall near Elfkarleby in Sweden (fig. 9), as also by the Rhonetrichter near Bellegarde in the French department de l’ Ain (pl. 53, fig. 6) Streams of water sometimes often pierce rocks and form great gateways, over which pass the so-called natural bridges, constituted by the portion remaining. A remarkable instance of this is to be found in the valley of Icomonzo in Columbia (pl. 49, fig. 4). The natural bridge near Lexington, Virginia, is another illustration.

Water in the form of ice often produces great disturbing effects, and, indeed, has every title to being considered as a rock species. The descent of large glacier masses to the edge of the sea, and their accumulation along the shore, give rise to Icebergs, which are sometimes very dangerous to navigation, both in their original locality and in more tropical regions, to which they are carried by ocean currents or winds. It is to glaciers and icebergs that many of the phenomena of diluvial scratches, transportation of boulders and rocks, &c., are ascribed. Pl. 52, fig. 1, is a view of icebergs and ice-cliffs in the antarctic regions.

Abnormal Rock Masses

Abnormal masses are essentially different from the normal, in standing in regular order of succession neither to the latter nor to each other. They pierce through the normal rocks in the most diversified directions, and traverse them just as they traverse each other. In this interpenetration of each other by abnormal masses, it is possible to decide in many cases as to the relative ages; but the determination is always more difficult than in the case of normal rocks, and the same species may in one region be older, and in another younger, than those with which it is associated. This relation is beautifully exhibited by granite, which was considered by the older geologists to be the most ancient of all rocks. This supposition is most certainly true in many cases, yet granite is known more recent than the cretaceous system. Granite is frequently met with that has been traversed by newer granite; then if we find that the older of these granites is more recent than, for instance, the variegated sandstone, the newer must be still more recent. In many cases, however, it cannot be determined whether it be newer than the Muschelkalk, Keuper, Jura, or chalk, which are supported by the variegated sandstone.

Where abnormal masses come in contact with normal, so that the latter are traversed by the former, changes are generally produced, as well with respect to the extensive as the intensive peculiarities of the latter. The changes of external character have reference to the position of the strata, which may be elevated, upheaved, displaced, broken, or even inverted; those of internal character relate to alterations in the petrographical character of the rocks, as the chemical constitution and the condition of aggregation. Sometimes abnormal masses, in penetrating normal, take up a position between the strata of the latter, and thus acquire a pseudo-stratification which it may require considerable acuteness to detect.

Masses often occur which can be referred neither to normal nor abnormal: they owe to the latter their origin, and have been stratified by water; such are various conglomerates, as basalt, trachyte, leucitophyr, and other conglomerates, &c. In general, abnormal masses belong to the isonomic division; they occasionally are heteronomic, in being accompanied by rocks of the litter character. They are always crystalline, and where this is not evident in the fresh fracture, the weathered surface will frequently exhibit it. A glissy texture is highly characteristic of an igneous origin; where this is noi exhibited, other phenomena may lead to the same conclusion.

The mineral substances composing the abnormal masses are principally silictes, or compounds of silicic acid. Among these may be mentioned feldspar, mica, pyroxene, and amphibole. Pure silicic acid in the form of quart, is of rarer occurrence as an essential component, and that only in the older masses. Oxydes of iron occupy a conspicuous place, these making their appearance in the more recent abnormal rocks, in proportion as the silicic acid disappears.

The vhole character of abnormal masses is opposed to their possession of organs remains. Haussman has distinguished three orders according to the relative ages, as far as this can be ascertained.

Plutonic Rocks

Plutonic rocks are embraced within the region of the primary or bottom, and middle series, and are the cause of many of the changes to which these have been subjected. The principal rock species are granite, syenite, eurite, and other porphyries; amphibolic rocks, especially greenstone; pyroxenes, as euphotide, cabase, trap, serpentine, &c. They are not found in definite succession, and the same species often belongs to different formations.

Granite Rocks

Granite has often permanent characters over considerable extents. It everywhere exhibits the same grain, the same color, &c.; on its confines, however, variations are sometimes met with; it becomes porphyritic, incloses foreign minerals, among which are schorl and pistacite (thallite), exhibits a weathered exterior, and is often colored red by oxyde of iron. Granite frequently forms masses of great extent, as the Riesengebirge and Erzgebirge of central Europe, and sometimes occurs in a more isolated condition, as in the Brocken of the Hartz. It sometimes penetrates in between abnormal masses, as of gneiss, and frequently forms veins both in normal and abnormal rocks. It not unfrequently happens that granite is traversed by a newer granite; this has then, in most cases, a coarser grain and a different color from the old. The cleavage of granite is frequently very decidedly parallelopipedal, being most clearly exhibited in weathering, where the blocks present an appearance not dissimilar to a sack of wool. These blocks are sometimes tabular, as also globular, and combined with a concentrically scaly cleavage (on the Rehberg in the Hartz). The rock faces of granite are exceedingly picturesque and imposing when the mass is of great amount. The valleys then appear like deep fissures, with the sides presenting a most magnificent appearance. The mountain forms are most generally spherical in outline, with the above-mentioned bag-like rocks strewn around in every direction on the summits; needles and peaks are sometimes exhibited under similar circumstances.

Granite, upon the whole, is very rich in veins, the contents of which, are very various. Some contain mineral substances resembling one or more of the natural constituents, as feldspar and quartz; some, again, are occupied by a newer granite, by syenite, porphyry, greenstone, trap, and basalt. Foreign substances are frequently met with in these veins, as dumb veins (these without metallic ores) filled with barytes and fluor spar; on veins, with gold inclosed in quartz or masked by sulphuret of iron; silver and silver ores, with galena, specular iron, haematite, oxyde of manganese and tinstone, tungsten, apatite, mispickel, &c. These veins not seldom extend into normal masses, or are found at the confines of the two.

The weathering of granite is very noteworthy, and furnishes products of great importance both to agriculture and the arts. The feldspar, for instance, is decomposed by the continuous influence of the atmosphere, of carbonic acid, and of water. The crystalline portions are clothed with a loose, soft, opake, dull crust, which sinks deeper and deeper, gradually transforming the entire feldspar. The increasing volume exerts a mechanical influence on the granite in crumbling it to pieces, this taking place first at the sharp corners and edges of the cleavage, and subsequently penetrating still deeper. The feldspar thus affected, will, on examination, be found to have been partially converted into a bisilicate of potassa, by the combination of an additional quantity of silicic acid from the quartz, the bisilicate is more readily soluble in water. The alumina, with the diminished amount of silex, and a proportion of water, remain behind, and form a white, fine-grained, unctuous mass, kaolin, which is an important ingredient in pottery. The soluble silicate of potassa furnishes the potassa so necessary to the plant, and is represented by the formula \(\dot{\mathrm{K}}^3\:\dddot{\mathrm{Si}}^8\), while the aluminous silicate = \(\dddot{\mathrm{Al}}^3\:\dddot{\mathrm{Si}}^4+6\:\dot{\mathrm{H}}\). All feldspathic rocks experience the same action, as weiss-stein, gneiss, syenite, some feldspathic porphyries, &c. The magnetic polarity of some granitic rocks is somewhat remarkable. The observation was first made at Ilsenstein in the Hartz, subsequently on the Schnarcherklippe, also in the Hartz. Granite occurs in many different periods of normal deposits. In Sweden it is older than the transition slate, which is shown from the fact that it had upheaved the gneiss, and become melted into it, and that then the transition slate rocks were deposited in horizontal nonconformable strata. The granite of Esterelle in Provence is older than the red sandstone. In Sweden, some granites are younger than the transition slates; they have broken through the old red sandstone and overlie it. There are granites in England which are newer than the carboniferous, but older than the new red sandstone. In the Alps, granites overlie the Jura, and, in the Pyrenees, have broken through the cretaceous. The granite is often traversed by other plutonic rocks, as by syenite, eurite, porphyry, and trap; it often itself traverses syenite and various pyroxenes.

The phenomena accompanying the presence of granite clearly testify to its plutonic origin. Masses in its vicinity are generally of greater density than those further removed; grauwacke is changed into hornfels, clay slate into silicious slate, and sandstone into quartz rock. The relation borne by hornfels to granite is frequently very interesting. The former often constitutes a thin covering for the latter, inclosing it in an envelope. Again, it sometimes constitutes a cap to the granite. This is well seen on the Achtermanns heights in the Hartz. Not far from there, on the Rehberg cliff, the granite has passed in veins into hornfels. Sometimes single fragments of the granite are inclosed by hornfels, and the reverse; and if pieces of limestone are present, they are changed into marble. Granite is most extensively distributed: it forms a constituent of almost all mountains throughout the entire earth. Exceptions to the general rule do, however, occur, as it is not found in the Sierra Nevada and the Jura chain.

Syenite Rock

Syenite, although small in quantity in proportion to granite, yet stands in precise relation to it. It is frequently found in connexion with normal masses, and only rarely occurs isolated. When in considerable quantity, it is generally shattered, furrowed by deep valleys, whose sides are studded with rocks. The rock features of syenite are much like those of granite; the cleavage also is similar, although less regular.

Syenite is not unfrequently traversed by veins of newer syenite, of different petrographical character. In these veins, again, are sometimes found other veins of very interesting minerals, as elaeolite, beryl, pyrochlore, and polymygnite. There are also veins of trap, dumb veins, and ore veins with gold and platinum, brown iron-stone, and quartz.

The weathering of feldspar in syenite proceeds much in the same manner as in granite. The hornblende resists the decomposition longest, and thus gives rise to a roughness of the stone. Even this substance, however, is forced to yield in time to chemical forces, and a dark ferruginous soil is the result, as favorable to vegetation as that from granite.

Syenite most frequently occurs in feldspathiferous pseudo-strata of the bottom series, as in gneiss. It is also found in nests and veins in the transition slate. Syenite has been met with of more recent origin than the oolite and chalk.

In its other relations syenite is very similar to granite, especially in the accompanying phenomena. The distribution is much more limited than that of granite. It is found principally in Sweden, Norway, Finland, Germany, France, on Mount Sinai, in Greenland, in South and North America, and in some other parts of the earth.

Porphyry Rocks

Under this head belong porphyries of various kinds. The principal are: eurite-porphyry, claystone-porphyry, and silicious porphyry. They have generally parallelopipedal cleavage, although both columnar and globular forms occur. Quartz is often separated in a pure state; which, however, is not the case on the newer porphyries, from which, then, they are sometimes distinguished as quartziferous porphyry. Porphyry rocks generally resist well the action of the atmosphere. The mountains present themselves sometimes as sharp combs, acute pyramids or cones; sometimes as high dome-shaped elevations (porphyry mountain near Kreuznach, pl. 53, fig. 4), with a greater or less quantity of loose rocks and stones about the base.

The internal uniformity of porphyry masses is sometimes interrupted by nests or beds of kaolin or magnetic iron-stone. Veins are not of frequent occurrence. They are stanniferous, ferriferous, manganiferous, plumbiferous, argentiferous, &c., with various gangues.

Eurite-, clay-, and hornstone-porphyry, both in the bottom series and in the transition slate, occur in nests, veins, and beds between the strata; the formation most frequently consists of porphyry that is younger than the carboniferous, but older than the zechstein. The occurrence of porphyry younger than the variegated sandstone has not yet been satisfactorily indicated.

A porphyritic breccia sometimes presents itself as a product of attrition, connected with the elevation of these abnormal masses. The contiguous rocks are shattered, and the pieces cemented together by an earthy mass, the result of the consequent grinding together of the rocks.

The porphyries already adduced are found in prominent positions on the Scandinavian peninsula, in Great Britain, Germany, France, the Altai Mountains, Mount Sinai, and in various parts of America.

In Germany it occurs in the Hartz, in Westphalia, in the trans-Rhenish Palatinate, in the Odenwald, the Schwarzwald, in Saxony, Silesia, &c.

Amphibolic Rocks

Of these, diorite is the most conspicuous. It forms veins rather than independent masses. Where it occurs of greater extent, it exhibits rough mountain forms, a character conspicuously impressed upon the individual rocks. This, as in syenite, is caused by the decomposition of the feldspathic substance, most generally albite, thus leaving the harder hornblende in the form of projecting asperities.

Pyroxene Rocks

These form both single smaller block masses, and entire connected series of mountains, as also veins and injected pseudo-morphous strata between normal strata; they also constitute caps extending over other rocks. The cleavage takes place in various ways; in curved surfaces, in acute angled parallelopipedons and in columns, which latter often exhibit a striking similarity to those of basalt, and are especially peculiar to trap. The curved surfaces frequently exhibited by diabase are often globular, with concentric scaly lamination. Diabase of this character is not un frequently called ball rock.

A particular modification of diabase, the shell-stone, has often a stratiform appearance, or pseudo-stratification. The external features of the pyroxenes have many peculiarities. Where they form large masses, the mountains present steep declivities, studded with rugged rocks; where they are surrounded by normal masses, the single portions project in a dome form from them. Diabase amygdaloid is intimately connected with compact diabase, and gradually passes into it; the amygdaloid occurs specially in the external portions of the rock, the compact occupying the nucleus.

Veins of no inconsiderable importance traverse the pyroxenes, containing haematite, specular iron, quartz, chalcedony, &c. The trap, trap porphyry, and trap amygdaloid, exhibit veins in which manganese minerals occur with barytes, calcareous spar, and arragonite. Copper and selenium ores are found in veins between diabase and the transition slate, at Lerbach, Tilkerode, and Zorge. in the Hartz.

The pyroxene rocks are not readily weathered, but form, in time, a tolerably good ferruginous soil. The rocks most frequently penetrate the strata of the transition slate, and of the bottom series. The most trap, trap porphyry, and trap amygdaloids, as also some euphotides, are newer than the carboniferous formation, in overlying the limestones of the latter. Some plutonic pyroxenes appear to be newer than the variegated sandstone. Of other masses, it penetrates syenite, granite, eurite-porphyry and allied rocks, and is often traversed by granite.

Among accessory phenomena may be cited the occurrence of breccias, of oxyde of iron, of silicious rocks, as hornstone, whet and silicious slate, which often, injected into limestone, give to it the appearance of marble; also, the occurrence of gypsum in the vicinity of diabase.

Pyroxene rocks are of very general distribution; they are found in Sweden, Norway, Great Britain, Germany, in the Pyrenees, France, south coast of Spain, in the Apennines, and in North America.

Among these masses are also to be enumerated schiller spar, ophite, and serpentine. Ophite, in particular, occurs where serpentine stands in connexion with marble or dolomite. Serpentine is extensively distributed in Turkey, where it has many external features in common with euphotide.

Serpentine is exceedingly interesting, from the mineral substances which it incloses. Among these are chromate of iron, used in the preparation of the pigments of chrome: also, platinum, pyrites, masses of asbestos, broncite, picrolite, chalcedony, opal, &c.

The weathering of serpentine proceeds very slowly, but is much facilitated by the dissemination of iron pyrites. The resulting sulphuric acid combines with a portion of the magnesia contained in the serpentine, and forms sulphate of magnesia or epsom salts.

Volcanoid Rocks

The volcanoid masses coincide more with the volcanic than with the plutonic: they are intermediate between the two, and traverse the latter, but are never pierced by them. The pyrotypic character is very distinctly impressed on them, and while pure silex diminishes in quantity, oxyde of iron occurs in so much greater proportion. The principal rock species are trachyte, phonolite (clinkstone), and basalt.

Trachyte

This is often accompanied by subordinate masses of pearl, pitch, and pumice-stone and obsidian, as also by hornstone and claystone-porphyry, and possesses very striking mountain forms, of a bell shape, or that of a cone either acute or truncated. Trachytic rocks lie either in linear series one after another, or they are grouped concentrically. They sometimes attain a considerable height, as the Mont d’Or in Auvergne. Its absolute height is 3000 feet, and the entire elevation above the level of the sea 5800 feet. The cleavage is sometimes conformable to the mountain outline; often, however, columnar or bench formed, as on the Wolkenburg in the Siebengebirge (pl. 49, fig. 6).

The veins of trachyte are often of importance; some of them contain gold and silver.

Trachyte masses emerge in the most different normal formations; they are known in the transition slate, and some are known more recent than the chalk and the newest tertiary formations. In Auvergne they traverse granite, and in other countries phonolite and basalt, with which they not rarely exhibit unmistakable indications of a common origin and time of occurrence.

Phonolite (Clinkstone)

This is intermediate between trachyte and basalt, and is, in most cases, presented as clinkstone-porphyry. It forms a great part of the Rhone mountain, where it is exhibited in forms similar to those of basalt, namely, in spherical masses, or in caps extending over other rocks. Its cleavages are generally flat and tabular, although columns likewise occur. The principal accompanying mineral substances are zeolites.

Phonolite forms greater or less masses in Höhgau, in Bohemia, in the Rhongebirge (in Thuringia), in the Siebengebirge, and in France

Basalt

This embraces true basalt, basalt amygdaloid, anamesite, dolerite, and basalt conglomerate, which, as modifications of one and the same rock, pass insensibly one into the other. Basalt occupies the most important place among the volcanoid rocks; its mountains may not be so high as those or trachyte, but are much more extended. It also constitutes veins and penetrations between strata of stratified masses. Dome-shaped mountains or hills are of frequent occurrence, as also those which are truncated or actually conical. Basalt veins are of various thickness, and are frequently in such connexion with the caps, as to render it satisfactorily evident that the vein is simply the pipe or space through which the molten mass has been injected to cover the superior strata.

Basalts exhibit picturesque rock formation, especially when brought in contact with water, or where earlier cataclysms have given rise to valleys. This is the case on the Island of Staffa (pl. 52, fig. 6), on the Island of Tahiti (pl. 51, fig. 6), and in other places.

Basalt occurs under the most diversified forms, representing, in this respect, nearly all the rocks of which mention has already been made. Thus we may see the most beautifully regular columns of various lengths and diameter; globular and spheroidal formations are often combined with concentric shelly cleavage.

Basaltic amygdaloid is found on the exterior of the rocks in caps or veins, where bubbles of gas may distend the melted matter, leaving cavities on the cooling of the mass. These cavities subsequently became filled with the most beautiful crystallization. Small veins not unfrequently consist entirely of amygdaloid.

Basaltic masses are found as well on the bottom series as upon the newest tertiary; they traverse older plutonic, or other volcanoid rocks, as also ore veins, although they themselves never contain these. Where basalts occur, they are generally combined with basalt conglomerate, which is often of great thickness. It generally lies at the foot, or on the slopes of basaltic mountains, and where it is tufaceous, it appears stratified, sometimes even alternating with strata of brown coal and woody opal. Where the basalt stands in contact with stratified rocks, the latter are influenced in the most varied manner, in a manner entirely attributable to the elevated temperature. Sand is converted into quartz grit, limestone into marble; silicious substances, as jasper, chalcedony, and hornstone, are forced into sandstone and lime, and partly melted together. Gypsum likewise is found in the vicinity of basalt.

A magnetic polarity has been ascertained to exist in basalt as well as in granite, dependent, in all probability, upon the magnetic oxyde of iron.

Basalt experiences a chemical decomposition, which is first indicated by a rusty coating to- the surface. The soil resulting from such decomposition is often very fertile, and calculated to the formation of swamps.

Basalt is distributed in Greenland, Iceland, on the Faroes, in the Hebrides and in Ireland, also in Germany, France, Spain, Portugal, Italy, North Africa, America, on the South Sea Islands, and in the East Indies. In Germany it is seen on the Leine, on the Weser, in Hesse, in the Rhineland about Bonn and Coblentz, in Thuringia, in the Rhongebirge, in Lausatia, Bohemia, Hohgau, &c.

Volcanic Rocks

Volcanoes, among the most conspicuous of all geological phenomena, stand in the same relation to the other abnormal masses as the top rocks do to the normal or stratified; they come immediately after the volcanoid masses, from which, however, they are essentially different, although in many cases it is quite difficult to draw the line of distinction.

By volcanoes or burning mountains are generally to be understood conical elevations, with an apical concavity, in communication, by a deep hole or throat, with the interior of the earth, through which liquid masses and solid rocks are ejected from time to time. The concavity or crater, and the descending funnel, are characteristic of the volcano, although these features may be masked by the crumbling and falling in of the sides. Pl. 44, fig. 9, is a section of a volcanic cone. Volcanoes may be divided into two classes, active and extinct, with an intermediate form, the Solfatara, where there is a continued emission of sulphurous matters.

Active volcanoes have often long periods of rest or intermission, after which they again become active, and are so much the more devastating. An example of this is found in Vesuvius, whose eruptive history begins from the time of Pliny, and continues to the present time. Although there probably were eruptions anterior to the time of Pliny, yet of such we possess no record.

Extinct volcanoes are much more numerous than active; they occur in many countries, and even in Germany in the Rhine region. The outbreaks of very many belong to ante-historical periods; no doubt, however, can arise, as to their true character, as most still exhibit traces of former activity in the shape of lava currents, &c. These lava streams, in many cases, are exceedingly altered by the action of weathering and of water; the craters, also, may either be in good preservation, or marked by the same atmospheric influences.

Pseudo-volcanic must be distinguished from truly volcanic phenomena. The two often exhibit great similarity, but are effects of different causes. Among these pseudo-volcanic exhibitions belong those terrestrial ignitions effected by the combustion of oxydizable substances in coal beds, such as are met with in various portions of England, Germany, and North America.

At Zwickau in Saxony, the ground is heated to such a degree, that all the conditions necessary to the existence of a hot-house are answered, by simply erecting an edifice on the heated portion. In these hot-houses, without additional artificial warmth, such tropical fruits as pine-apples, &c., may readily be reared. At Dudley, in England, the subterranean fire may be seen through fissures in the rocks in dark nights : smoke and vapors habitually rise out of these fissures, and are visible at all times, especially in wet weather. Pl. 52, fig. 4, represents the burning mountain near Duttweiler. A conspicuous illustration of the same phenomenon is exhibited in Schuylkill county, Pennsylvania, where the rubbish from an extensive coal mine became ignited, and finally the whole bed. The result of such combustion is naturally to effect transformations in the neighboring rocks, bearing a considerable resemblance to those produced by regular abnormal masses while incandescent. At Epterode, at the foot of the Meissner, in Hesse, there is a hill originally consisting of tertiary clay, which has been changed by the combustion of a coal bed into a slag-like compact rock, the so called porcelain jasper.

It was upon these subterranean combustions that Werner based his volcanic theory, which, however, meets with no support in the present state of science.

Volcanoes are found in all parts of the world, and are confined to no particular level. They sometimes crown the ridges of widely extended mountain chains, as on the South American Andes; sometimes they rise up in mountainous or hilly regions and planes, and even from the bottom of the sea. The carefully conducted investigations of recent observers have shown that they are almost always in the neighborhood of the sea. Thus in Chili, in Peru, and in Mexico, they extend along the coast at no great distance; in Europe, they lie along the Mediterranean Sea and the Atlantic Ocean. Most generally they occur on islands, many of which, unquestionably, owe their very origin to the elevation of the incumbent volcano. There are volcanoes, however, which lie entirely within the main land, among which may be mentioned the extinct cones in China, France, and on the Rhine. Still, we may readily reconcile this fact with the general Vaw of the contiguity of volcanoes to the sea, by reflecting that the sea level, as can be satisfactorily shown in some cases, might have been so different from what it is now, as even to have washed the very bases of the cones. Pl. 47, fig. 1, presents a comprehensive view of the volcanic regions of the globe; fig. 2 is a chart of European volcanoes, fig. 3, of those of lower Italy, all after Berghaus. On the latter, the earthquake region of Calabria and Sicily is indicated by the dark lines; that of Naples by a dotted outline. A fuller explanation of these charts will be found under the head of Physical Geography.

The shape of volcanoes is in general that of a more or less perfect, acute, or truncated cone. The ejected matters are heaped up around the mouth or crater. One of the most beautiful cones of this character is the Pic de Teyde on Teneriffe, as also Cotopaxi in the Andes chain. The height of volcanoes varies considerably, sometimes not reaching to the level of the sea, and at others extending into the higher regions of the atmosphere. Thus Stromboli, on the Lipari Islands, attains a height of 2,687 feet; Etna, of 10,814; the Peak of Teneriffe, 12,172; Mauna Roa, 13,760, and Mauna Koa, 13,953 (Sandwich Islands); Tunguragua in Quito, 16,424; Popocatepetl, 17,717, and Orizaba, 17,374 (Mexico); Cotopaxi, 18,890; Antisana, 19,150; Pinchincha, 15,940; Hecla, 3,324; Vesuvius, 3,978; Mount St. Elias, in North Western America, 16,775; Awatsha, in Kamschatka, 9,600. These heights are all above the level of the sea. The absolute height of the scoria about volcanoes naturally depends upon the number of eruptions. In Vesuvius they occupy \(\frac{1}{3}\), in Pinchincha \(\frac{1}{10}\), and in the Peak of Teneriffe \(\frac{1}{22}\) of me entire cone. This part of the volcano, as forming the apex of the whole, naturally presents very steep sides of a mean inclination of 33° to 40°. The steepest parts of Vesuvius, of Jorullo, and of the Peak of Teneriffe, have an inclination of 40° to 42°.

The summit of the scoria cone is generally provided with a funnel-formed aperture, the crater. It is erroneous to suppose that the largest cones must necessarily have the largest craters; in fact, it would be more generally correct to say that the larger the cone the smaller the crater. The crater, generally circular, is of various diameters; that of Stromboli measures 50 feet, that of Vesuvius 1500 and over, of Etna 1250. The nearly elliptical crater of the Peak of Teneriffe has diameters of 200 and 300 feet, that of Popocatepetl 5000 and 4000. The largest known crater is that of Mauna Roa in the island of Hawaii; this is three and a half miles long, two and a half wide, and a thousand feet deep, large enough, in the language of Captain Wilkes, to accommodate the entire city of New York, leaving still an abundance of room.

The edge of the crater may also vary in character; it is generally, however, elevated like a wall, and descending nearly vertically towards the mouth (pl. 50, fig. 7, interior of the crater of Etna). It is often intersected by deep fissures, through which access may be had to the mouth. The depth of the crater of the Peak of Teneriffe amounts to 110–115 feet, that of Pinchincha to 1800, and that of Popocatepetl to 800–1000 feet.

The bottom of the crater is either simple or provided with various small cones of eruption, of which a greater or less number are in active operation. The crater of Kirauea (pl. 47, fig. 4), on the island of Hawaii, with a depth of 1000 feet, and a circumference of eight miles, has fifty of such small cones of eruptions; a night scene in this crater is shown in pl. 49, fig. 1.

Similar phenomena are exhibited in the crater of a volcano on the island of Hawaii (pl. 41, fig. 5). Some volcanic cones arc inclosed by a Avail of gentle slope outside, but dipping abruptly towards the cone. Such is the Somma which surrounds Vesuvius, and is probably the wall of the ancient crater as it existed in the time of the Romans. Pl. 45, fig. 4, is a supposed view of Vesuvius in the time of Pliny: fig. 5, as seen at the present day.

The lava streams which accompany a volcanic eruption do not generally pour over the edge of the crater, but escape through fissures which may be formed in the sides. Among the most important volcanic products may be mentioned, lavas, pumice, various ejected matters, volcanic conglomerates, sublimates, and rocks altered by heat and vapors.

By the term lava is meant all volcanic matters exhibiting a liquid molten character. Lavas have a very different appearance under different circumstances; which difference, however, is rather accidental than essential. Even the same species of rock may exist under very different forms; thus pumice-stone is nothing else than trachyte in a frothy condition, and obsidian is the same, of a glassy and compact texture. Lavas may exist; under the various forms of fillings, of strata, and as streams. The fillings generally occur in fissures through which an eruption has taken place, and present a striking resemblance to some of the veins we have already considered. Lava strata are pseudo-morphous, deriving their stratiform character by penetrating between true strata. This, however, is not always the case; it may happen that an earlier stream of lava, with the usual incumbent scoria and ashes, is covered by one of subsequent origin, and this, in like manner, by a third, &c., so that an alternation of stratiform masses of lavas and scoria may exist. The peculiarities of the masses are seen most conspicuously in the lava streams. These streams flow down the sides of the cone as far as the amount of the lava and the peculiarities of the soil may allow.

The greatest lava stream of Mount Vesuvius had a length of 47,500 feet. That which took place in 1805, was 16,735 feet long, with a breadth of 8,542, and depth of 30–40 feet.

Lava currents must naturally obey the laws which regulate other liquid masses. Should they meet with some obstruction in their course, such as a mountain or large rock, they divide into arms; flowing in a trough) or channel they fill it up; pouring over precipitous descents, they form fiery cascades. They frequently run into the sea, and there sometimes form conspicuous features. Thus the lava stream which poured forth from Vesuvius, in 1794, ran into the sea, and formed a peninsula, eight hundred feet broad and seventeen feet high above the level of the sea. The surface of molten lavas soon cools, and forms a stiff crust beneath which the liquid mass still flows on. If this interior current be interrupted, it frequently breaks through the incumbent crust, and piles up on the surface, this sometimes giving rise to lava arches such as are met with in Iceland (pl. 52, fig. 3). When the lava currents pour into lakes, they sometimes dry these up; an example of this is furnished by the volcano Krabla in Iceland, whose inner crater is represented in pl. 50, fig. 6. It first attracted attention by its mighty eruption, May 17, 1724. Among the phenomena of this eruption, which continued for six years, was the advance of a single lava stream to Lake My-vatn, a distance of nearly six miles, and drying it up almost entirely.

The cooled lava has generally a very rough surface, caused by superficial bubbles and scoria. The interior is either amorphous, or separated in tabular, columnar, or spheroidal form. The spheroidal state is frequently exhibited by obsidian, which occurs in great extent in Iceland. The bubbles or vesicular cavities which are seen in the outer portions of the current, and which are not rarely heaped up so as to form large masses of pumice, are ellipsoids of greater or less perfection, and with the longer axis parallel to the direction of the stream.

Lava presents itself in general under three forms; as glassy, as stony, and as crystalline. The glassy has arisen from a very rapid cooling, and is furthest removed from the crystalline. It has a highly conchoidal and sharp-edged fracture, is brittle, more or less transparent, and of a vitreous lustre. Stony lava has a strong resemblance to stone ware; it is of earthy dull fracture, generally entirely opake, and intermediate between glassy and crystalline lava.

Lava streams may be referred to three classes : trachytic, basaltic, and leucitophyric. Trachyte lavas are characterized by feldspar or its minerals, which, however, is only recognisable when the aggregation state of the rock is decidedly crystalline. Crystalline trachytic lava forms a true trachyte, which generally is of a light color, not seldom modified by the presence of hornblende, specular iron, micaceous iron, and true brown mica. It frequently passes into porphyrinic, so as sometimes to constitute a trachyte orphyry. The stony trachytic lava is often granulated, and contains vesicles and particles of glassy feldspar. The glassy is formed by pumices and obsidian; it is either pure, or contains porphyritically separated particles of feldspar.

Augite predominates in basaltic lava, accompanied by labradorite and various ferruginous minerals, for which reason these rocks are generally of a dark color. They are very similar to the true volcanic basalt, often so much so as to present no difference in petrographical character, this difference being only deducible from oreographical peculiarities. A true obsidian and pumice do not occur among the basaltic lavas, and a few glassy varieties of some similarity to these, are distinguishable by the simple blowpipe test that the former yield white, the latter dark globules on fusion. The crystalline granular basaltic lava exhibits a true dolerite, and for this reason is sometimes called dolerite lava: it characterizes Etna in particular. The stony lava is of a greyish black and brown color, with a compact vesicular, or slaggy interior. Here belong the Mühlstein of Niedermennig, not far from the Laacher Lake, as well as some basaltic lavas of Auvergne.

Leucitopliyr lava consists of a combination of augite with leucite, in which sometimes one substance prevails and sometimes another. It is the same leucitopliyr whose petrographical character Ave have already become acquainted with. It likewise embraces many other minerals which are not essential to its composition, as zeolite, sodalite, mica, micaceous iron, nepheline, harmotome, &c.; it occurs both crystalline and stony. The crystalline leucitophyr often contains perfect crystals (trapezohedra), whose tolerably equal dimensions and light color contrast remarkably with the black prisms of the augite.

The term “volcanic ejectamenta” includes everything thrown into the air by volcanic forces. They are of very different character, and vary not only in different volcanoes but in different eruptions of the same volcano. Under this head belong pieces of lava torn off from the interior of the throat or mouth of the volcano, and hurled out during the eruption; also, the so-called bombs or spheroidal lava masses, which, ejected into the air, have had a rotary motion communicated to them, and cool before reaching the ground. The form of these bombs is that of elliptical spheroids elevated at the equator and flattened at the poles, presenting a miniature resemblance to the terrestrial globe. Additional substances thrown out of the volcano are lava gravel; volcanic sand, consisting of crystalline particles of volcanic minerals; volcanic ashes, consisting of the dust of ground up rocks; volcanic threads produced from the lava like fine fibres from molten glass; finally, blocks of foreign rock species, as granite, gneiss, mica slate, dolomite, sandstone, and limestone, the latter, when inclosed by the lava, being partially or entirely converted into marble. These ejectamenta, after being deposited in an appropriate location, are frequently so acted upon by water as to become converted into volcanic conglomerate and volcanic tufa. They then appear stratified, and are distinguished according to the character of their components into trachyte conglomerate, trachyte tufa, basalt conglomerate, leucitophyr, conglomerate, and leucitophyr tufa; these, not unfrequently, are broken up into conspicuous rocks by subsequent convulsions, and are sometimes traversed by veins of lava.

Volcanic mud is produced by the union of volcanic ashes or dust with water, which, vaporiform while escaping from the mouth of the volcano, becomes condensed in the higher regions of the atmosphere, and descends in the form of rain, accompanied by thunder and lightning. Currents are sometimes produced under such circumstances, sufficient to devastate extended regions. These muddy waters not unfrequently accumulate in subterranean cavities; and by means of fissures in the sides of the mountains, are allowed to escape into the lower lands. According to Humboldt, discharges of mud never take place in the same manner as lava. The subterranean lakes sometimes contain a great number of fish, which are discharged with the water in which they live. These fish are, however, not peculiar to the subterranean waters, being found in the superficial lakes and streams. Thus Arges cyclopum, Val. (Pimelodus cyclopum, Hnmb.), and Brontes prenadilla, Val., are emitted from the volcanoes of Tunguaragua and Cotopaxi in South America.

Volcanic sublimates are not only of great extent, but are often of great importance to mineralogists. These are bodies which continue in the form of vapor until condensed into the solid state by cooling, in which case they generally coat the walls of the crater and the cavities in the lava with a crystallization of greater or less perfection. Volcanic sublimations are met with not only in active volcanoes, but also in such as are nearly extinct, or the Solfataras. The principal sublimates are. combinations of chlorine, sulphur and sulphuric acid combinations, and metallic oxydes.

The gaseous exhalations and deposits from volcanic waters stand in intimate connexion with these sublimates. Among the gases are carbonic acid, sulphurous acid, and chloride of hydrogen or hydrochloric acid. Sulphites are formed by the action of the sulphurous acid upon the neighboring rocks, which by further oxydation, are converted into sulphates. In this manner are formed sulphate of ammonia, sulphate of soda (glauber salts), sulphate of alumina, sulphate of iron, alum, and alum stone. The deposits from volcanic waters consist generally of silicious sinter, more rarely of borax. Naphtha springs appear likewise to stand in a certain connexion with volcanoes.

Besides the primary phenomena of volcanoes, as lava currents and ejectamenta, there are others of secondary or derivative character, as earthquakes. A striking feature presented to us in our examination of a volcano mountain, is the great homogeneity of its character; furthermore, that its shape is almost always conical, with a crater upon the summit, and the entire mass different in petrographical character from the region above which it projects. All these circumstances, with the fact that no crater is found upon the summit of a mountain not volcanic, clearly evince that an exceedingly intimate connexion must exist between the formation of the crater with its central throat and that of the mountain itself. The mountain in which the crater is situated must first have originated by volcanic upheaving; eruptions then followed, whose ejecta accumulated and gradually increased the size of the cone. After this heaping up around the mouth of the volcano had increased to a certain amount, the internal forces were no longer capable of raising the volcanic matters to the level of the mouth; fissures were then formed in the sides of the mountain, through which the lava was emitted. These phenomena are met with in the highest volcanoes. The formation of volcanic mountains has indeed been actually observed; striking instances of which are exhibited in the case of Monte-Nuovo near Naples, of Jorullo in Mexico, and of various volcanic islands elevated in the sea.

The formation of Monte-Nuovo took place in September of 1538. (See the chart of the Bay of Naples and its volcanic district, pl. 45, fig. 8.) It rose up from a plain of inconsiderable elevation above the level of the sea, after premonitory quakings of the earth of two years’ duration. On the 28th of September flames burst forth from the earth, the ground cracked open, and a considerable quantity of water escaped, while the sea retreated about three hundred paces. On the following day, soon after the sun of a fiery red had set behind the western waters, a cavity opened near the sea, which vomited forth flame, smoke, dust, and pumice, which, in the course of two days, heaped up a mountain of about 8000 feet in circumference, and of considerable height, with a crater on the summit. Shortly afterwards, this outbreak ceased, and the whole became quiet. Subsequently followed other powerful eruptions, but at the present time, Monte-Nuovo belongs to extinct volcanoes, overgrown with the most luxuriant vegetation, and whose crater exhibits only traces of its original condition.

The elevation of Jorullo in Mexico, as described by Alexander von Humboldt, must have been an awfully sublime spectacle. The locality of this stupendous exhibition was a highly cultivated plan, elevated about 2000 feet above the level of the sea, with loosely scattered blocks of basalt upon the surface. In June of 1759, a terrible bellowing was heard, with ominous earthquake shocks. This lasted sixty days, until, towards the end of September, all danger appeared to have vanished. But suddenly, in the night of the 18th and 19th of this month, the sounds recommenced, and an extent of land of nearly four square miles was covered with scoria and lava, by means of eruptions, which did not cease until February, 1760. Six volcanic cones were formed, the central one, or Jorullo, attaining an elevation of 1600 feet above the level of the plain. Thousands of small cones, called hornitos, are dotted over the region, produced by the heaping up of dome-shaped masses of lava by the disengagement of gaseous matters. Some have supposed that part, at least, of the general elevation has been produced by the actual elevation of the plain, as on the surface of a gigantic bubble; this hypothesis, however, hardly appears to be substantiated by the physical features of the region. The six cones above referred to, were arranged along an immense fissure, extending from north-east to south-west. From this central fissure, with its subsequent ridge and six elevations, the volcanic masses slope at a general angle of 6° to the circumference of the tract. It is not probable that any material accession to the volcanic matter was experienced after the year 1760; at the present day, the greater portion of the plain is covered with a rich growth.

The elevation and disappearance of the island of Ferdinandea in the channel between Sicily and Africa, was a highly interesting phenomenon. The water of the sea was thrown into great waves, gigantic columns of smoke escaped, the neighboring coasts experienced earthquake shocks, and an island rose suddenly from the troubled sea. It was on the 28th of June, 1831, that earthquakes were experienced in Sciacca, on the southern coast of Sicily, accompanied by a thundering noise. A British vessel in the vicinity experienced shocks, and vesicular dust was carried by the winds and deposited on the Sicilian coast. At break of day, on the 13th of July, up to which time the indications of volcanic phenomena were continued, the new volcano was first observed from Sciacca, emitting immense volumes of sulphurous acid, which annoyed the whole neighboring region. A few days after, an immense expanding column was observed to rise out of the mouth of the volcano, consisting of various ejecta, the more solid portions of which fell into the water with a hissing sound. Lightnings, accompanied by heavy thunder, illuminated the dark scene, whose horrors were heightened by subterranean explosions. On the 28th of September, when the mouth had ceased to emit anything except sulphurous vapors, Prevost, in company with some fellow-voyagers, visited the island, and remained upon it for several hours. He ascertained the circumference to amount to 2000 feet, and the highest point of the crater to extend to an elevation of 200 feet above the level of the sea. The lake which filled the crater, and which stood at the same level with the ocean, was about about 180 feet in diameter. Pl. 50, fig. 4, presents a view of the island, and fig. 5 one of the inner crater. The island subsequently began to sink, standing at the level of the sea at the end of September, until at the beginning of December it had entirely disappeared. Quite similar circumstances attended the elevation of a small volcanic island, in 1811, near St. Michael, one of the Azores; it disappeared subsequently, so that now there is a depth of eighty fathoms and more over the summit. A figure of the island, at the time of its elevation, is presented in pl. 50, fig. 2.

After the lightnings which accompany an eruption, and the subterranean explosions, have ceased to excite terror and apprehension in the hearts of the beholders, there sometimes arise luminous columns of fire, veiled in a black vapor. Nature appears then for a moment to be appeased and at rest: but new volcanic agencies commence which may be far more dangerous than any which have preceded. These are the mofettes, or gas springs, which, emitting noxious gases, such as carbonic acid, diffuse deadly poison throughout the entire region. While many of these soon disappear, others remain permanent for a long time, as the Grotto del Cane, near Naples (pl. 51, fig. 7), or else exist as acid springs in combination with water.

Earthquakes generally announce an eruption; they are movements of the solid crust of the earth, whose cause or origin lies concealed within her bowels. A precise connexion between the two series of phenomena may not be strictly established, although such relation can in many cases be substantiated. The motions of the earth which constitute an earthquake are either horizontal and vertical, or rotatory: they are greatest in the centre of the field of influence, decreasing gradually to its borders. The extent of surface affected in a single system of earthquake is very various, and sometimes of great amount; in the earthquake of Lisbon it covered the half of Europe, and as far as the West Indies. Deep fissures are often formed by earthquakes, such as those near Polistena in Calabria (pl. 44, fig. 15), and sometimes circular cavities, as in the plain of Rosarno (fig. 16), produced by the earthquake of 1783.

The greater number of hot springs belong to volcanic exhibitions, as is well shown by their occurrence, in most cases, in volcanic regions. The most striking of these phenomena is to be found in the case of the Geyser of Iceland (pl. 50, fig. 1), a periodical spring, whose waters at a boiling heat are ejected to a considerable height in the air. The opening of the spring, or of the crater, lies on a hill consisting of silicious sinter, which the water had previously contained in the form of soluble silex. This action is shown in pl. 44, fig. 17. Iceland is especially rich in other volcanic phenomena of extraordinary grandeur. Pl. 45, fig. 10, is a chart representing the Iceland volcanic region. In the south of Iceland is the high cone of Hecla, and the snow and ice-covered volcano of Eyafiel. Of this volcano as of the island of Westmann, in front of it, a view is presented in pl. 44, fig. 18. They lie on the southern exit of a wide valley, which is continued between trachytic masses. Northwardly this valley runs towards a group of volcanoes constituted by Krabla, Leirhnukur, and others, while the elevated Orafejokul to the east rears its proud head towards the sky.

A phenomenon, sometimes called an aerial volcano, is not unfrequently found to accompany earthquakes. This is constituted by a small cone of eruption, consisting of accumulated mud masses, often impregnated with saline waters. From the mouth is emitted gaseous matter, generally hydrogen, which is alternately inflamed and extinguished. The air volcanoes of Turbaco in Columbia (pl. 50, fig. 3), are very conspicuous in this respect.

Leopold von Buch makes a distinction between volcanic centres and volcanic lines. The first kind consist of a central volcano surrounded by several smaller ones, which are pretty equally distributed in every direction. Mount Etna, in Sicily, is a central volcano, with its smaller cones of eruption arranged about its base. In the view of Etna on pl. 45, fig. 6, a, indicates Montagnuola; 6, Torre del Filosofo; c, the highest point of the mountain; d, Lepra; e, Finocchio; f, Capra; g, the cone of 1811; h, the Cima del Asino; i, Musara; k, Zoccolara; l, Rocca de Calanna. On the volcanic chart of the same region (fig. 9), 1 indicates the volcanic formation, 2 the newer pliocene, and 3 the latter formation combined with the former. Fig. 7 represents the Campi Phlegrsei; a, Montenuovo; b, Monte Barbaro; c, Solfatara; d, Lake Lucrine; e, Lake Averno; f, the city of Pozzuoli; and g, the tongue of land Baja.

Linear volcanic series are seen in high development on the elevated crest of the Cordilleras de los Andes, extending over a line of many hundred miles, with individulal cones succeeding each other at greater or less intervals.

Various hypotheses with regard to volcanoes have been propounded by the earlier geologists, few of which are now considered to exhibit any, show of probability. One of the least objectionable of modern theories is that of Housmann, who considers lavas to be nothing else than products of oxydation of bodies previously unoxydized, which exist at the confines between the molten nucleus of the earth and the hard crust. That the interior of the earth must consist of denser masses than the exterior, is sufficiently evinced by the fact, that the mean density of the entire earth amounts to 4.70 (5.50 according to Cavendish), and that of the outer crust to but 3.00. When these unoxydized bodies, which consist principally of potassium, sodium, aluminum, silicon, iron, &c, come into contact with water, this is decomposed, and oxydes are formed with the evolution of great quantities of heat and hydrogen; the latter, mixed with oxygen of the air, produces the explosions. The sea-water penetrating at a great depth, appears to be the principal source of the water required; a fact well illustrated, by the situation of volcanoes within a moderate distance of the sea, and confirmed by the occurrence of chlorine combinations, of nitrogenous substances and bitumen. The steam may be produced from the water existing in the abyss, and also by the re-combination of hydrogen and oxygen of the atmosphere. The oxydes thus produced are melted together in the hearth of the gigantic furnace by means of heat derived from the central fires, as also from the oxydation itself, and in the form of lavas are vomited up over the blooming fields, carrying death and destruction in their path.

The Surface of the Earth in General

In considering the external form of the earth, and of the relations between normal and abnormal masses, we have seen brought in review before us mountains and valleys, land and water. The mountain is seen to be nothing else than a slight elevation above the general level, and the watery surface only a filling up of a depression. Yet, however fortuitous all these features may appear to be, an attentive observation reveals to us the existence of certain laws influencing the general result.

The elevations in the form of mountain chains contribute very essentially to the character of our globe. These had certainly never arisen but for the longitudinal disturbance by plutonic masses of the original horizontal position of the rock strata. The position of the strata thus appears to be dependent upon plutonic masses, as may be observed in almost all mountain chains: the cases are indeed rare where this conclusion is unsupported by actual exhibition of these masses themselves. Even if certain changes are not attributable to such masses, they may belong to some of their concomitants, such as the vapors produced in the interior of the earth. Pl. 47,fig. 7, presents a comparative view of the principal mountain heights of the old world; fig. 8 does the same for the new.

Volcanoid and volcanic masses are of much less importance in influencing the general shape of the earth; they only form domes, single mountains and hills, upon localities furnished to them by plutonic rocks.

It is exceedingly difficult, if not absolutely impossible, to picture to our minds the condition of the earth at its first period of development. Speculative geology or geogeny may indeed endeavor to penetrate to the bottom of all the phenomena and facts which are furnished to it by geognosy as a purely empirical science: it may seek to develope the causes which have produced such mighty effects, and thus pass itself step by step to the primeval condition of our planet, to speculative hypotheses as to its original shape, to the laws according to which its fashioning proceeded, to the causes upon which depended the successive changes on its surface. And these speculations may not be disregarded, but their application must be made with all due caution, that the proper and legitimate bounds of reasoning be not overstepped. According to Laplace, the earth, with the entire solar system, at one time, was a vastly diffused nebulous mass, set in rotary motion, and, by successive subdivisions, furnishing the material for the individual bodies of our planetary world. These masses of vapor must have possessed a temperature sufficient to retain all the solid components in the gaseous condition. Such is the hypothesis of astronomy; geology takes it up at the time when the vapor is supposed condensed into a liquid, still molten mass, to which an ellipsoidal shape is given by a rapid rotation about an axis. In cooling, the earth becomes invested by a solid crust, upon which the aqueous vapors of the atmosphere are condensed. In proportion as the nucleus of the earth parts with its heat by radiation into space, must contractions of its volume take place; and the space between the inner kernel and the outer shell being thus of considerable amount, the incumbent mass breaks in and permits the access of atmospheric air to the fires below. The effects exhibit themselves in volcanic reaction, by means of which certain portions of land become elevated above the general level. A repetition of such depressions and elevations results in the elevation of entire continents with their mountain ranges and the collection of the great body of water in the interspaces. The ascending vapors from this water become condensed to clouds, fall in the form of rain, and, after partially saturating the more elevated regions, burst out into springs, whose combination produces rivers and lakes, all emptying continually into the great body of ocean, by a more or less circuitous course. The sea, as well as the fresh water, acting on these continents, exerts a destructive influence upon the harder portions; and the finer particles resulting from their action are spread out and deposited as strata in some quiet bay or lake. Smaller fragments, subdivided by concussion, attrition, atmospheric agencies, or other causes, are also carried down to form conglomerates. The masses arranged thus horizontally, and hardening by the incumbent weight or other influences into solid rocks, are elevated afresh, and new lines of demarcation are drawn between the waters and the dry land. We may safely consider such operations of aqueous and igneous causes as sufficiently capable of producing all the geological features of our globe.