THEORY OF THE EARTH. 265 



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 ap- 

 pearance more than once as we proceed. 



Our fossil lam an tins differ from those known to 

 exist at present, in having the head more elonga- 

 ted, and of a different form *. Their ribs, which 

 are easily recognised by their being of a thick and 

 rounded form, and of dense texture, are not of rare 

 occurrence in our different provinces. 



With regard to the fossil morse, small frag- 

 ments only have as yet been found of it, which 

 are insufficient for characterising the species f. 



It is only in the strata that have succeeded the 

 coarse limestone, or, at most, those which may 

 have been of contemporaneous formation with it, 

 but deposited in fresh-water lakes, that the class 

 of land mammifera begins to shew itself in any 

 quantity. 



I consider as belonging to the same period, and 



* Researches, vol. v. part ii. p. 266. 



t Id. vol. v. part i. p. 234 ; and part ii. p. 521. 



