The ferruginous sands, placed in England above the chalk, contain abundance of crocodiles, tortoises, megalosauri, and especially a reptile which presents a character quite peculiar, in as much as its teeth appear worn, like those of our herbivorous mammifera. To Mr Mantell of Lewes, in Sussex, we are indebted for the discovery of this latter animal, as well as of other large reptiles belonging to the sands lying beneath the chalk. He has named it _Iguanodon_[261]. In the chalk itself there are only reptiles to be seen: there are found in it remains of tortoises and crocodiles. The famous tufaceous quarries of the mountain of St Peter, near Maestricht, which belong to the chalk formation, along with very large sea tortoises, and a multitude of marine shells and zoophytes, have afforded a genus of lizards not less gigantic than the megalosaurus, which has become celebrated by the researches of Camper, and the figures which Faujas has given of its bones, in his history of that mountain. It was upwards of five and twenty feet long; its large jaws were armed with very strong conical teeth, a little arcuate, and marked with a ridge, and it had also some of these teeth in the palate. Upwards of a hundred and thirty vertebræ were counted in its spine; they were convex before, and concave behind. Its tail was deep and flat, and formed a large vertical oar (or organ of swimming).[262] Mr Conybeare has recently proposed to name it _Mosasaurus_. The clays and lignites which cover the upper part of the chalk, I have only found to contain crocodiles[263]; and I have every reason to think that the lignites which in Switzerland have afforded beaver and mastodon bones, belong to a later epoch. Nor has it been at an earlier period than that of the coarse limestone which rests upon these clays that I have begun to find bones of mammifera; and still do they all belong to marine mammifera, to dolphins of unknown species, lamantins and morses. Among the dolphins, there is one, the muzzle of which, more elongated than that of any known species, has the lower jaw united in a considerable part of its length, nearly as in a gavial. It was found near Dax by the late president of Borda[264]. Another species, from the cliffs of the Department de l’Orne, has the muzzle also long, but somewhat differently shaped[265]. The entire genus of lamantins is at the present day confined to the seas of the torrid zone; and that of the morses, of which only a single living species is known to exist, is limited to the frozen ocean. Yet we find skeletons of these two genera side by side in the coarse limestone strata of the middle of France; and this association of species, the nearest allied to which are, at the present day, found in opposite zones, will again make its appearance more than once as we proceed.