THE SURFACE OF THE GLOBE. 143 



It was upwards of twenty-five feet long ; its great jaws were armed 

 with very strong teeth, conical, rather arched and ridged, and it had 

 also some of these teeth in the palate. There were more than a hun- 

 dred and thirty vertebrae in its spine, convex in front and concave be- 

 hind. Its tail was high and broad, and formed a large vertical oar. 

 Mr. Conybeare has recently proposed to call it the mosasaurus. 



The clays and lignites, which are above the chalk, have only produced 

 crocodiles ; and I have every reason to conclude that the lignites in 

 Switzerland, in which have been found the bones of the beaver and 

 mastodon, belong to a more recent period. It is only in the coarse 

 limestone which rests on these clays that I have first found the bones 

 of mammifera ; and even these belong to marine mammifera, to un- 

 known dolphins, to lamantins and morses. 



Amongst the dolphins, there is one whose muzzle, more lengthened 

 than in any known species, had the lower jaw united to an extent 

 nearly equal to that of a gavial. It was found near Dax, by the late 

 President of Borda. 



Another of the rocks in the department of Orne, has also a long 

 muzzle, but rather differently shaped. 



The whole genus of lamantines is now marine, and inhabit the seas 

 of the torrid zone ; and that of the morses, of whom we have but one 

 living species, is confined to the icy sea. However, we find the ske- 

 leton of these two species together in the layers of the coarse lime- 

 stone of the middle of France ; and this union of species, of which the 

 most similar are now in opposite zones, will again occur in our re- 

 searches more than once. 



Our fossil lamantins differ from the known lamantins, by having 

 a head more elongated, and otherwise constructed. Their ribs, easily 

 recognised by their rounded thickness and by the density of their tex- 

 ture, are not rare in our different provinces. 



As to the fossil morse, we have as yet only fragments insufficient 

 to characterise the species. 



It is only in the layers which have succeeded the coarse limestone, 

 or at most in thosewhich might have been formed at the same time with 

 it but deposited in the fresh-water lakes, that the class of land mam- 

 mifera begins to show itself in any abundance. 



I regard as belonging to the same age, and as having lived at the 

 same time, but perhaps in different situations, those animals whose 

 remains are buried in the molasse and the ancient beds of gravel in 

 the south of France ; in the gypsum layers mingled with limestone, 

 similar to those in the environs of Paris and Aix, and in the marly 



