THE EOCENE OF EUROPE AND NORTH AMERICA 119 



being the name first applied by Haj^den ' to a group of beds of this age 

 near Evanston, western Wyoming. This Evanston 'Wasatch' represents 

 the earUest phase (corresponding with the Sparnacian and Lower Ypresian of 

 Europe), a more recent phase of the same fauna being contained in the 

 Wind River Formation of central Wyoming. The animals which tie 

 these vastly extended deposits together are Coryphodon, Eohippus (the 

 earliest type of American horse), Phenacodus, and Palceonictis. In the 

 Wind River (corresponding with the Upper Ypresian of Europe), Bathyopsis, 

 a new member of the Order Amblypoda appears. 



The contrast which the life of the Coryphodon Zone of the Wasatch 

 and Wind River exhibits to the very archaic and chiefly Mesozoic fauna of 

 the underlying and- earliest Torrejon and Puerco formations (p. Ill) ren- 

 ders this one of the most striking of modernizations in the whole American 

 Caenozoic. 



The archaic and modern mammals are in these North American Spar- 

 nacian and liower Ypresian beds thoroughly mingled; the former still pre- 

 dominate in the number of genera and species; they also predominate in 

 size, Coryphodon and Phenacodus and the carnivorous creodonts being the 

 largest mammals of the period. 



The mammals belonging to the modernized orders are inferior in size 

 and in number of species, but prove to be mechanically superior both in 

 their foot and tooth structure, and of higher intelligence. 



The summary of this mingled fauna is as follows: 



Summary of Wasatch Genera and Species 



Multituberculate marsupials (Plagiaulacida?) 

 Placental mammals of archaic type 

 Placental mammals with modern affinities 



In this calculation the Insectivora are included among the archaic 

 forms, the Primates, or Lemuroidea, among the modern. Naturally a 

 sharp line cannot be drawn between orders, and the above table only repre- 

 sents the momentous change in a broad way. As compared with the 

 summaries on pp. 107-8, the contrast is sufficiently striking. 



Formations of the Coryphodon Zone. — Phase I. As shown in the accom- 

 panying map, the chief exposures in the central Rocky Mountain region 

 are as follows: (1) the typical 'Wasatch' group of Hayden, or more re- 

 strictedly the 'Knight Formation 'of Veatch, 1,750 feet; (2) the Wasatch 

 of the Black Buttes (= Bitter Creek of Powell, = Vermillion Creek of 

 King, 1878), in the Washakie Basin, Wyoming; (3) the 'Wasatch' of the 



• Haydon, F. V., Geological Report of the Exploration of the Yellowstone and Missouri 

 Rivers, by F. V. Hayden, assistant to Col. William F. Raynolds, U. S. Engineers, Washing- 

 ton, 1869. 



