X PREFACE. 



his researches lead, of the new genera and spe- 

 cies which these have been the means of dis- 

 covering, and of the different formations in 

 which they are contained. Some naturalists, 

 as La Mark, having maintained that the pre- 

 sent existing races of quadrupeds are mere 

 modifications or varieties of those ancient races 

 which we now find in a fossil state, modifica- 

 tions which may have been produced by change 

 of climate, and other local circumstances, and 

 since brought to the present great difference 

 by the operation of similar causes during a long 

 succession of ages, Cuvier shows that the dif- 

 ference between the fossil species and those 

 which now exist, is bounded by certain limits ; 

 that these limits are a great deal more exten- 

 sive than those which now distinguish the va- 

 rieties of the same species ; and, consequently, 

 that the extinct species of quadrupeds are not 

 varieties of the present existing species. This 

 very interesting discussion naturally leads our 

 author to state the proofs of the recent popu- 

 lation of the world; of the comparatively 



