98 THEORY OF THE EARTH. 



quiet continuance of the sea upon our continents. 

 Above them, indeed, there are found formations 

 containing shells and other marine productions ; 

 but these consist of collections of transported mat- 

 ters, sand, marls, sandstones, and clays, which ra- 

 ther indicate transportations that have taken 

 place with more or less violence, than strata formed 

 by tranquil deposition ; and, if there be some 

 rocky and regular strata of pretty considerable 

 magnitude, beneath or above these transported 

 matters, they generally exhibit indications of ha- 

 ving been deposited from fresh water. 



Almost all the known bones of viviparous qua- 

 drupeds, therefore, have been found either in those 

 fresh-water formations, or in the alluvial forma- 

 tions ; and consequently there is every reason to 

 conclude that these quadrupeds have only begun 

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

 strata of our earth, after the last retreat of the 

 sea but one, and during the state of things that 

 preceded its last irruption. 



But there is also an order in the disposition of 

 these bones with regard to each other ; and this 

 order further announces a very remarkable succes- 

 sion in the appearance of the different species. 

 All the genera which are now unknown, the Pa- 

 laeotheria, Anaplotheria, &c., with the position of 

 which we are thoroughly acquainted, belong to 

 the oldest of the formations of which we are now 



