PALEONTOLOGY SINCE CUVIER. 71 



equivalents of the Eocene, Miocene, and Pli- 

 ocene of Europe, although usually so considered 

 and known by the same names ; but, in general, 

 the fauna of each appears to be older than that of 

 its corresponding representative in the other hemi- 

 sphere an important fact not hitherto recognised.' 



The area of the life which extended throughout 

 the Tertiary period, and showed, in part, a closer 

 connection than can be proved in the case of 

 Europe, lies along both sides of the Eocky Moun- 

 tains. To the west more especially in the region 

 of the Green Eiver it extends up to the height 

 of the Great Salt Lake. It is more extensive 

 still to the east, where the so-called Bad Lands 

 (Mauvaises terres) in the state of Dakota are the 

 most productive centre. 



Leidy's work on the ancient fauna of Nebraska, 

 which marks an epoch in the palaeontology of the 

 United States, has been completed by his investi- 

 gations on the extinct vertebrates of the Western 

 Territories. 1 Since then not a year has passed 

 without Cope, and Marsh especially, bringing to 

 light new branches of this rich tree of knowledge. 3 



1 Leidy, ' Contributions to the Extinct Vertebrate Fauna of 

 the Western Territories,' United States Geographical Society. 

 Washington, 1873. 



2 We do not yet possess any detailed account of this incom 



