CENOzoic (interior). 287 
roundiDg land is composed. The cave deposits of the Megalonyx 
beds are of course highly calcareous. The Eocene beds, at least 
those of the "Wasatch and Bridger series, resemble the Laramie in 
the abundance of small calcareous and ferruginous concretions 
which they contain. 
EOCENE SYSTEM. 
The Eocene formations of the interior of North America are 
as follows : 
Diplacodon beds, 
Bridger, 
Windriver, 
Wasatch. 
These formations are clearly successive in their relations. 
There are two others, contemporary with one or more of these, 
whose characters are due to special physical causes. They are the 
Amyzon beds, 
Greeuriver shales. 
They differ from each other in the following faunal peculiarities : 
Wasatch. — Mammalia. Presence of Tseniodonta, Condy- 
larthra, and Pantodonta. Absence of Tillodonta, Dinocerata, 
Palaeosyops, Hyrachyus, Amynodon, Achasnodon, Triplopus, 
and suilline and selenodont Artiodactyla. 
This formation is characteristic of the region between the 
Rocky Mountains proper and the Wasatches, and has three prin- 
cipal areas. The most southern is in Northwestern New Mexico ; 
the middle tract is in Southwestern Wyoming and Northeastern 
Utah ; the third tract is in Northwestern Wyoming, on the Big 
Horn River. 
Thickness in Northwestern New Mexico (Cope), . 2500 feet 
Thickness in Southwestern Wyoming (Hayden), . 1500 " 
Thickness in Northwestern Wyoming (Wortman), . 4000 " 
WiNDRiVER. — Mammalia. Presence of Condylarthra, Tfe- 
niodonta, Pantodonta, Dinocerata, Palseosyops, and Hyrachyus. 
This fauna indicates the transition between the Wasatch and 
Bridger, since types are here associated which are elsewhere 
peculiar to the two horizons named. Thus, of the above zoolog- 
ical divisions the following are otherwise exclusively Wasatch : 
Tseniodonta and Pantodonta. The remaining ones are Bridger, 
