172 THE GEOGRAPHY OF MAMMALS 



the deposits the genera can all be definitely assigned to 

 existing orders. 



The earliest mammals that have been found in North 

 America come from the Trias of North Carolina, but 

 neither these nor any of the other mammalian remains 

 of the Secondary Period tend to assist the geographical 

 problems involved, or are of importance in the present 

 juncture. 



With the oldest Tertiary beds an entirely new fauna 

 appears, and furnishes us with remains of forms belonging 

 to various orders of which no traces can be found in the 

 earlier Secondary deposits. The following is a short list of 

 these deposits, together with their European equivalents, so 

 far as they can be ascertained : — 



Lower Eocene 



Puerco beds of New Mexico. 

 Wasatch beds of Wyoming, Utah, and New 

 Mexico. 



Mid-Eocene . . Bridger beds of Wyoming. 



Upper Eocene. . Uintah beds of Utah and Wyoming. 



Lower Miocene . White-river beds of Nebraska, Dakota, Colo- 

 rado, and Wyoming. 



Mid-Miocene . . John-Day beds of Oregon, Nevada, and 

 Washington. 



Pliocene . . . Loup- Fork beds of Nebraska, Colorado, Wyo- 

 ming, Kansas, and New Mexico. 



Late Pliocene . Equus beds of Western and South-Western 

 States, and Megalonyx beds of Eastern 

 States. 



In the lowest Eocene beds, not only the Genera, but 

 even the Orders of mammals are in almost every case 

 different from those at present existing. The greater 

 number of these belong to two orders — Creodontia and 

 Condylarthra ; the former the progenitors of the modern 

 Carnivora, the latter of the existing Ungulata. These 



