OLIGOCENE OF EUROPE, NORTH AFRICA, AND NORTH AMERICA 225 



First Phase of the Upper OUgocene, Leptauchenia-Protoceras Zone 



Geologic conditions. — The upper part of the Brule Clays of the White 

 River Group in the Great Badlands immediately and conformably overlie 

 the Oreodon Zone. Correlated with these are widespread deposits in 

 northeastern Colorado and in North Dakota, indicating a continuation of 



Fig. 111. -I'hc Ipiicr ( )li<_'(iciiii' fniii-hnriu'd luiiiinanf tN'pc of the I'rdtorcras Zone. 

 Above : Protocerax chased by the Hght-Hinbed saber-tooth Dinirtis. After oriniiial l)y CharU-s 

 R. Knight. Below : Skeleton of Protoceras celer. Both in the American Museum of Natural 

 History. 



