The great beds of coal, and the trunks of palms and ferns of which they preserve the impressions, although they afford evidence of the existence of dry land, and of a vegetation no longer confined to the waters, do not yet shew bones of quadrupeds, not even of oviparous quadrupeds. It is only a little above this, in the bituminous copper-slates, that we see the first traces of them; and, what is very remarkable, the first quadrupeds are reptiles of the family of lizards, very much resembling the large monitors which live at the present day in the torrid zone. Several individuals of this kind have been found in the mines of Thuringia[247], among innumerable fishes of a genus now unknown, but which, from its relations to the genera of our days, appears to have lived in fresh water. Every body knows that the monitors are also fresh water animals. A little higher is the limestone called Alpine, and resting upon it the shell-limestone, so rich in entrochites and encrinites, which forms the basis of a great part of Germany and Lorraine. In it have been found skeletons of a very large sea-tortoise, the shells of which might have been from six to eight feet in length; and those of another oviparous quadruped of the family of lizards, of a large size, and with a very sharp muzzle[248]. Rising still through sandstones, which present only vegetable impressions of large arundinaceæ, bamboos, palms, and other monocotyledonous plants, we come to the different strata of the deposit which has been named the Jura limestone, on account of its forming the principal nucleus of that chain of mountains. It is here that the class of Reptiles assumes its full development, and shews itself under the most varied forms and gigantic sizes. The middle part, which is composed of oolites and lias, or of grey sandstone containing gryphites, contains the remains of two genera, the most extraordinary of all, which have combined the characters of the class of oviparous quadrupeds with organs of motion similar to those of the cetacea.