100 THEORY OF THE EARTH. 



deposits formed on the sides of rivers, or on the 

 bottoms of ancient pools or marshes now dried up, 

 or in the substance of beds of peat, or in the fis- 

 sures and caverns of some rocks; or, lastly, at 

 small depths below the surface, in places where 

 they may have been buried by the falling down 

 of debris, or even by the hand of man ; and their 

 superficial position renders these bones, although 

 the most recent of all, almost always the worst 

 preserved. 



It must not, however, be thought that this clas- 

 sification of the various geological positions of fos- 

 sil remains, is as certain as that of the species, or 

 that it is equally capable of demonstration. There 

 are numerous reasons which prevent this from be- 

 ing the case. 



In the first place, all my determinations of spe- 

 cies have been made upon the bones themselves, 

 or by means of good figures ; whereas it has been 

 impossible for me personally to examine all the 

 places in which these bones have been discovered. 

 I have very frequently been obliged to content 

 myself with vague and ambiguous accounts, given 

 by people who were not themselves well aware of 

 what it was necessary to observe ; and, more fre- 

 quently still, I have been unable to procure any 

 information whatever on the subject. 



Secondly, these repositories of organic remains 

 are subject to infinitely greater doubts, than the 



