106 University of California Publications in Geology [V L - 7 



as compared with the Pre-Glacial. The Post-glacial epoch was 

 characterized by an ameliorated climate and a depression of the 

 land surface. Great river floods and large lakes were the result 

 of this amelioration, and extensive fluviatile and lacustrine de- 

 posits appear, while the previously restricted species of verte- 

 brates spread out over parts of the country that were formerly 

 covered by the ice cap. 



The faunas of the time are divided by Osborn into three life- 

 zones which are distributed through the Pleistocene, but do not 

 coincide with the three time divisions as given above. They do 

 not necessarily represent consecutive faunas, but rather faunas 

 from different topographic divisions which, in some respects, 

 overlap each other, though in the main consecutive. Charac- 

 teristic mammals have given the names to these zones as follows : 

 Equus Zone, a plains fauna partly earlier than and partly 

 synchronous with the second, the Megalonyx Zone, which was 

 a forest and meadow fauna mainly of mid-Pleistocene time. The 

 third, or Ovibos Zone, is an impoverished fauna, perhaps cor- 

 responding with the Arctic and Tundra period of Europe and 

 synchronous with the last great glacial advance, the period of 

 maximum glaciation, which is recorded in the great terminal 

 moraine. 



RELATIONS OF SEVERAL PLEISTOCENE MAMMALIAN HORIZONS; ADAPTED 



FROM OSBORN 



Equus Zone Megalonyx Zone 



6 Kansas Pleistocene, several 9 Big Bone Lick, Ken. 



localities. 8 Samwel Cave, Calif. 



5 Lake Lahontan, Nev. 7 Potter Creek Cave, Calif. 



4 Fossil Lake, Ore. 6 Washtucna Lake, Wash. 



3 Eock Creek, Texas. 5 Rancho La Brea, Calif. 



2 Hay Springs, Neb. 4 Ashley Eiver, S. Carolina. 



1 Peace Creek, Fla., Late Plio- 3 Frankstown Cave, Penn. 



cene or Early Pleistocene. 2 Port Kennedy Cave, Penn. 



1 Afton Junction, Iowa. 1st in- 

 terglacial stage. 



Ovibos Zone 

 4 -Alaska Ground Ice. 

 3 Conard Fissure, Ark. 

 2 Scattered middle west. 

 1 Big Bone Lick, Ken. 



