CORRELATION AND PALEOGEOGRAPHY 245 



the new Ealston formation contains a mammal resembling Bathtjopsis of 

 the typical Wind Kiver; also a number of more primitive species of 

 Wasatch type. 



The annectant life zones between this sub-Wasatch and the well known 

 Torrejon, Fort Union (see Knowlton/'^ 1909), and Piierco fauna? all 

 remain to be discovered. When these are discovered, as they surely will 

 be, we may claim for the American Eocene the unique distinction of 

 presenting a perfectly continuous life chain of mammals from the base to 

 the sunamit. 



Oligocene 



No less important is the remarkable sequence from Lower Eocene to 

 Lower Oligocene discovered by Granger on Beaver Divide, Fremont 

 County, Wyoming. Here, overlying unmistakable "Wind Eiver beds,'' 

 are brown depositions probably of "Bridger" age, so identified because 

 above them lie true depositions of "Uinta" age containing the highly 

 characteristic forms Diplacodon, Amynodon, Protoreodon, Camelodon. 

 These were identified through the presence of the rhinoceros Amynodon 

 intermedius. Still higher are true depositions of the basal Oligocene 

 epoch identified by the equally characteristic species Titanotherium 

 heloceras. 



In the true Oligocene of the Western plains little progress has been 

 made beyond the classic subdivisions established many years ago by Leidy 

 (1869), Hatcher (1893), and Wortman (1893), into Lower, or Titano- 

 therium zone, Middle, or Oreodon zone, and L^pper, Protoceras and Lep- 

 tauchenia zones. 



The faunistic succession of the Oligocene has, however, been continued 

 with great geologic precision in the John Day of Oregon, by Mcrriam 

 (1091, 1906) and Sinclair.^® Here, again, we meet the Leptauchenm 

 zone, uppermost member of the White Eiver series, continued above into 

 the Diceratherium zone, which in turn is capped by the Promerycoclicerus 

 zone. 



Here quite arbitrarily we mark the transition from the Oligocene to 

 the Lower Miocene. Promerycocliocrns happens to be an abundant and 

 highly characteristic oreodont. It is associated with many other charac- 

 teristic species, so that when Promerycochoerus is again found along the 



^^ F. H. Knowlton : The Stratigraphic Relations and Paleontology of the "Hell Creek 

 Beds," "Ceratops Beds" and Equivalents, and their Reference to the Fort Union Forma- 

 tion. Proceedings of the Washington Acadeni.v of Science, vol. xi. no. ;i, 1000. pp.170-2:^'^. 



" W. .T. Sinclair and .T. C. Merriam : Tertiary Faunas of the John Day Region. Publi- 

 cations of the University of California, Department of Geology, vol. 5, no. 11, 1907, pp. 

 171-205. 



