Argillaceous Oxide of Iron

These seem common in marly and gravelly land, and are abundant at Shotover hill and its neighbourhood, where they are situated so as to assist in forming the fine yellow ochre of so great value as a pigment. They vary extremely in their shape, sometimes branching like a stag’s horn, or a branch of a tree, and have been taken for such petrified. They are often coated concentrically, imitating, as it were, the Medulla, Liber, Cortex, and Cuticle. it may seem that the moisture in passing through loosish marl has been impregnated with the oxide of iron, and, periodically drying, leaves the marl and oxide of iron concentrated; which forms the coating, according to the looseness of the earth. They sometimes concentrate to a ball, but at other times have only one or two coatings.

The upper figure is from Charlton in Kent, and had the remains of a shell of the Turbo kind in it. The inside of the screw is covered with minute crystals of carbonate of lime: tab. 62. 63. There are other impressions of shells about it.

The left-hand figure has the form of a pebble with a lightish ferruginous ochre on the inside, and a dark crust.

The right-hand figure had loose pieces of ochre in it, of different colours, pinkish, &c., and they sometimes have wet marl and water in them. Such are called Enhydros by Sir J. Hill. The specimen came from Moushold Heath, near Norwich.