causes. 



82 THEORY OF THE EARTH. 



as resulting from general causes ; and its investi- 

 gation may be considered as affording one of the 

 best means for discovering the nature of these 



Difficulty of determining the Fossil Bones of 

 Quadrupeds. 



If this study is more satisfactory in its results 

 than that of other fossil remains of animals, it is 

 also beset with more numerous difficulties. Fos- 

 sil shells usually present themselves in an entire 

 state, and with all the characters requisite for 

 comparing them with their analogous species, 

 preserved in the collections or figured in the works 

 of naturalists. Even fishes present their skele- 

 ton more or less entire ; the general form of their 

 body is almost always distinguishable, and most 

 commonly, also, their generic and specific charac- 

 ters, which are drawn from their solid parts. 

 In quadrupeds, on the contrary, even should the 

 skeleton be found entire, it would be difficult to 

 apply to it characters derived, for the most part, 

 from the hair, the colours, and other marks which 

 have disappeared previous to their incrustation. 

 It is even excessively rare to find a fossil skeleton 

 approaching in any considerable degree to a com- 

 plete state. The strata, for the most part, only 

 contain separate bones, scattered confusedly, and al- 

 most always broken, and reduced to fragments; and 



