OLIGOCENE OF EUROPE, NORTH AFRICA, AND NORTH AMERICA 207 



A ••<< Porcupine Butte 

 „ VOLCANIC ASH LAYER 



'^^v 



Aferycocharnti 



Fromer ycot 

 /orx 





iFpper ■ ffrsodon , Zone 



9^^^l32;=ffiu.fei^s;;£^£^5-J:'°°"'-AR layer" -^cir^rjr 



%. \ ^^■^^^XotvSli;; Oreodon '/. 



Stcneofiber 

 Prom erycoch a-rus 



L f'p tnurh en in 



Protoreras 



Oreodon 



(upper) 



Oreodon 



(middle) 



, 100 



1 i-i H H i-i i-i 



ZOO 



300 



400 FEET 



By permission of the American Museum of Natural History. 



Fig. 96. — Panoramic view of the Oligocene and Miocene exposures on the south side of the 

 White River, South Dakota. After Oshorn. 



