116 THEORY OF THE EARTH. 



verns of certain rocks, or at small depths below 

 the present surface, in places where they may have 

 been overwhelmed by debris, or even buried by 

 man : And, although these bones are the most re- 

 cent of all, they are almost always, owing to their 

 superficial situation, the worst preserved. 



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

 sification of the various mineral repositories is as 

 certain as that of the species, and that it has near- 

 ly the same character of demonstration. Many 

 reasons might be assigned to show that this could 

 not be the case. All the determinations of spe- 

 cies have been made, either by means of the bones 

 themselves, or from good figures ; whereas it has 

 been impossible for me personally to examine the 

 places in which these bones were found. Indeed 

 I have often been reduced to the necessity of satis- 

 fying myself with vague and ambiguous accounts, 

 given by persons who did not know well what was 

 necessary to be noticed ; and I have still more fre- 

 quently been unable to procure any information 

 whatever on the subject. 



Secondly, these mineral repositories are subject 

 to infinitely greater doubts in regard to their suc- 

 cessive formations, than are the fossil bones re- 

 specting their arrangement and determination. 

 The same formation may seem recent in those 

 places where it happens to be superficial, and 

 ancient where it has been covered over by sue- 



