112 THEORY OF THE EARTH* 



tween these fossil species and those which still ex* 

 ist upon the earth. 



The laws already recognised with respect to 

 these relations are very distinct and satisfactory. 



It is, in the first place, clearly ascertained, that 

 the oviparous quadrupeds are found considerably 

 earlier, or in more ancient strata, than those of the 

 viviparous class. Thus the crocodiles of Honfleur 

 and of England are found underneath the chalk. 

 The monitors of Thuringia would be still more an- 

 cient, if, according to the Wernerian school, the 

 copper-slate in which they are contained, along 

 with a great number of fishes supposed to have 

 belonged to fresh water, is to be placed among the 

 most ancient strata of the secondary or fla3tz for- 

 mations. The great alligators, or crocodiles, and 

 the tortoises of Maestricht, are found in the chalk 

 formation ; but these are both marine animals. 



This earliest appearance of fossil bones seems to 

 indicate, that dry lands and fresh waters must have 

 existed before the foundation of the chalk strata. 

 Yet neither at that early epoch, nor during the for- 

 mation of the chalk strata, nor even for a long pe- 

 riod afterwards, do we find any fossil remains of 

 mammiferous land-quadrupeds. 



We begin to find the bones of mammiferous sea- 

 animals, namely, of the lamantin and of seals, in 

 the coarse shell limestone which immediately co- 



