641 



familiarised with the zoological character of 

 rocks, a vast field of observation. To examine 

 these vestiges in the layers superposed as by 

 steps, the one on the other, is to study the 

 Faunes of different ages, and compare them to- 

 gether. The geography of animals traces the 

 limits in space according to the diversity of 

 climates, which determine the actual state of 

 vegetation on our planet. The geology of or- 

 ganised bodies, on the contrary, is a fragment 

 of the history of nature, taking the word his- 

 tory in its proper acceptation : it describes the 

 inhabitants of the earth according to the suc- 

 cession of time. We may recognise in mu- 

 seums, kinds and species ; but the Faunes of 

 different ages, the predominance of certain 

 shells, the numerical relations that characterize 

 the animal kingdom, and the vegetation of a 

 place, or of an epocha, should be studied in the 

 sight of those formations. It has long appeared 

 to me * that in the tropics as well as in the 

 temperate zone, univalve shells are much more 

 numerous (in their species) than bivalves. From 

 this superiority in number, the organic fossil 

 world furnishes, in every latitude, a further 

 analogy with the intertropical shells that now 

 live at the bottom of the ocean. In fact, Mi 



vox,, vi. 



* Essai geogn. p. 42. 



2 u 



