70 THE MAMMALIA. 



Pliocene fauna of Niobrara, whk-h lie buried in the 

 same ground as Nebraska, but in a later stratum 

 of sandstone, prove this in an even greater mea- 

 sure. Elephants, tapirs, and various species of 

 horses differ scarcely at all from those of the Old 

 AYorld: the boars, to judge from their dentition, 

 are descendants of the Palaeochoerus, &e., of the 

 European miocene deposits.' 



Even when these remarks of Biitimeyer were 

 written, we possessed an eminent work on the 

 Tertiary fauna of North America by Leidy. 1 But 

 since those days the discoveries made have been 

 so extraordinarily numerous, and the immense 

 variety of animals that lived there has proved so 

 much more varied than the European fauna, that 

 American investigators, headed by Cope and 

 Marsh, have come to the conclusion that America 

 was not colonised with Mammalia from the Old 

 World, but that the former gave Europe some 

 of its original superfluity ; even the theory ac- 

 cepted by Riitimeyer, that the Tertiary strata 

 of America were in part somewhat more recent 

 than ours, is proved to have been the reverse. 

 Marsh writes in 1877 : ' These natural divisions 

 (of the American Tertiary) are not the exact 



1 The Ancient Fauna of Nebraska, 1853. 



