Elastic Bitumen, or Fossil Caout-chou

In examining the Bitumens, it is difficult to say whether they pass from Naphta and Petroleum to Pitch and Asphaltum, by regular gradation, through the elastic kind, or not, as they seem to pass naturally from one to another without them. Most people would have been satisfied with the series had the elastic ones not ocurred. By accidentally breaking a mass of crystallized Carbonate of Lime, was found in a hollow a black mineral pitch, in a liquid state; see the left hand bottom figure. This has not become condensed and elastic, but not so much as the substance in the last figure. The crust or outer surface is brownish, with more elasticity, ad may be separated by the nail like the middle figure, which shows the outside and inside. The left hand figure shows also hollows in the centre of the outr crust, or external parts, something like the mouth of a minute crater; giving a strong idea of its having been once in a state of powerful ebullition from that hole. This is a darker-coloured Bitumen, possessed of greater elasticity than any that has been before noticed. Among specimens this should be placed as the darkest, and perhaps nearly the last of the elastic sorts. The next in this plate is a more indurated Bitumen, much resembling the last (at first sight), and which seems to have been in a state of ebullition, from the circular indentures remaining on the bubbles: see the right hand figures at the bottom. They are very neatly formed upon whitish cubic Fluor, and seem as if they had splashed about in falling; for they give the idea of having dropped on the surface of the crystals of the Fluor in a state of strong ebullition, perhaps more so than the former. Whatever is the cause, the nearer these substances approach combustion, the more they harden, and form the appearance of Asphaltum, which we suspect this substtance to be. This is from the same neighbourhood as the others, and is totally black all through. Fracture conchoidal and shining, destitute of any lighter illinitions, being perfectly opaque.