114 THEORY OP THE EARTH. 



the sea ; but these consist of alluvial materials, 

 sand, marie, sandstone, or clay, which rather indi- 

 cate transportations that have taken place with 

 some degree of violence, than strata formed by quiet 

 depositions ; and where some regular rocky strata, 

 of inconsiderable extent and thickness, appear 

 above or below these alluvial formations, they ge- 

 nerally bear the marks of having been deposited 

 from fresh water. 



All the known specimens of the bones of vivi- 

 parous land quadrupeds, have either been found 

 in these formations from fresh water, or in the al- 

 luvial formations ; whence there is every reason to 

 conclude that these animals have only begun to 

 exist, or at least to leave their remains in the strata 

 of our earth, since the last retreat of the sea but 

 one, and during that state of the world which pre- 

 ceded its last irruption. 



There is also a determinate order observable 

 in the disposition of these bones in regard to each 

 other, which indicates a very remarkable suc- 

 cession in the appearance of the different species* 

 All the genera which are now unknown as thepa- 

 Iceotheria, anaplotherid, &c. with the localities of 

 which we are thoroughly acquainted, are found in 

 the most ancient of those formations of which we 

 are now treating, or those which are placed direct- 

 ly over the coarse limestone strata. It is chiefly 

 they which occupy the regular strata that have 



