CORRELATION OF THE C EN O ZOIC 257 



The Wind River of central Wyoming together with the Lower 

 Huerfano near the Spanish Peaks of Colorado marks the upper life- 

 zone of Coryphodon and may prove to correspond closely with the 

 Ypresian of France. In the Rocky Mountains the Wind River is read- 

 ily distinguished by the survival of a number of characteristic Lower 

 Eocene types (Coryphodon, Pheitacodus) and the fresh arrival of a 

 number of equally characteristic Middle Eocene types (uintatheres, 

 titanotheres) . It is consequently an ideal transition fauna. Unfor- 

 tunately the formations believed to be of corresponding age in France 

 are poor in mammal remains. 



From this time on to the summit of the Eocene we are passing into 

 the third faunal phase, or divergence and independent evolution of 

 the life of Europe and America. Consequently close correlation is 

 almost impossible; at no period in the Tertiary were the Nearctic 

 and Palearctic faunas so widely separated. 



Middle. — With the American Bridger, 1,800 feet in thickness, we 

 enter the Middle Eocene and broadly compare the Lower Bridger 

 with the Lutetian and the Upper Bridger with the Bartonian of 

 France. The precise survey of the life-zones of the Bridger by 

 Granger and Matthew marks one of the greatest advances of recent 

 times. 



Similarly under the direction of the present writer the Washakie 

 of central Wyoming has been surveyed precisely by Granger, proving 

 that the Lower Washakie is identical in age and in its mammalian 

 life with the Upper Bridger and broadly corresponds with the Barto- 

 nian, or closing stage of the Middle Eocene of France. We are now 

 in the Uintatherium Zone, all the famous discoveries of Cope and 

 Marsh having been made at this level. Here belongs also the 

 beginning of the Uinta deposition of northern Utah. 



We now pass into the Eobasileus Zone of the Upper Washakie and 

 the Middle Uinta, in which the long-headed uintatheres described 

 by Cope as Eobasileus and Loxolo phodon occur mingled with remains 

 of highly specialized Eocene titanotheres. This is apparently the 

 lower level of the Upper Eocene and is broadly comparable with the 

 Ludian stage of France. 



Upper. — The succeeding Ligurian stage of France may be paral- 

 leled with the upper, or true Uinta, the Diplacodon Zone of Marsh. 



