CHAPTER III 



THE OLIGOCENE OF EUROPE, NORTH AFRICA, AND 

 NORTH AMERICA 



This period is sharply defined by great geographic revolutions as well 

 as great transformations in its animal and plant life. In Europe it opens 

 with the main elevation of the Pyrenees and is marked toward the close by 

 the initial elevation of the Alps (Fig. 13, p. 59). We are able to study the 

 Mammalia over a still wider geographic range. In America the princi])al 



Fig. 73. — Summit of the OlitiocciK^ or transition to the Miocciic. Lower: Brule ('lays, 

 or Leptauchenia Zone. Upper: Lower Rosebud, or Promerycochcerus Zone. Exposures ou 

 the south side of the White River, near Porcupine Creek. Photograph by American Museum 

 of Natural History, 1906. 



interest centers around our first knowledge of the life of the Great Plains 

 region, a vista we have not enjoyed previously because all our former 

 studies have been confined to the mammals of the mountain region. In 

 Europe the plains fauna still remains unknown. 



The most remarkable fact is the remingling by intermigration and by 

 fresh invasions of similar types from the north of the mammals of the New 

 and Old Worlds, so that Europe and western America again constitute a 

 single zoological region, or Holarctica. We thus enter the Fourth Faunal 

 Phase. 



N 177 



