Kimmeridge Clay.—The _Kimmeridge Clay_ consists, in great part, of a bituminous shale, sometimes forming an impure coal, several hundred feet in thickness. In some places in Wiltshire it much resembles peat; and the bituminous matter may have been, in part at least, derived from the decomposition of vegetables. But as impressions of plants are rare in these shales, which contain ammonites, oysters, and other marine shells, with skeletons of fish and saurians, the bitumen may perhaps be of animal origin. Some of the saurians (Pliosaurus) in Dorsetshire are among the most gigantic of their kind. Fig. 314: Cardium dissimile. Fig. 315: Ostrea expansa. Fig. 316: Cardium striatulum. Fig. 317: Ostrea deltoidea. Fig. 318: Gryphæa (Exogyra) virgula. Among the fossils, amounting to nearly 100 species, may be mentioned _Cardium striatulum_ (Fig. 316) and _Ostrea deltoidea_ (Fig. 317), the latter found in the Kimmeridge Clay throughout England and the north of France, and also in Scotland, near Brora. The _Gryphæa virgula_ (Fig. 318), also met with in the Kimmeridge Clay near Oxford, is so abundant in the Upper Oolite of parts of France as to have caused the deposit to be termed “marnes à gryphées virgules.” Near Clermont, in Argonne, a few leagues from St. Menehould, where these indurated marls crop out from beneath the Gault, I have seen them, on decomposing, leave the surface of every ploughed field literally strewed over with this fossil oyster. Fig. 319: Trigonellites latus. The _Trigonellites latus_ (_Aptychus_ of some authors) (Fig. 319) is also widely dispersed through this clay. The real nature of the shell, of which there are many species in oolitic rocks, is still a matter of conjecture. Some are of opinion that the two plates have been the gizzard of a cephalopod; others, that it may have formed a bivalve operculum of the same. Solenhofen Stone.—The celebrated lithographic stone of Solenhofen in Bavaria, appears to be of intermediate age between the Kimmeridge clay and the Coral Rag, presently to be described. It affords a remarkable example of the variety of fossils which may be preserved under favourable circumstances, and what delicate impressions of the tender parts of certain animals and plants may be retained where the sediment is of extreme fineness. Although the number of testacea in this slate is small, and the plants few, and those all marine, count Munster had determined no less than 237 species of fossils when I saw his collection in 1833; and among them no less than seven _species_ of flying reptiles or pterodactyls (see Fig. 320), six saurians, three tortoises, sixty species of fish, forty-six of crustacea, and twenty-six of insects. These insects, among which is a libellula, or dragon-fly, must have been blown out to sea, probably from the same land to which the pterodactyls, and other contemporaneous air-breathers, resorted. Fig. 320: Skeleton of Pterodactylus crassirostris.