106 University of California Publications in Geology [VoL 
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 Aretic 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—Washtuena Lake, Wash. 
3—Roeck Creek, Texas. 5—Rancho La Brea, Calif. 
2—Hay Springs, Neb. 4—Ashley River, 8. Carolina. 
1—Peace Creek, Fla., Late Plio- 3—Frankstown Cave, Penn. 
cene or Early Pleistocene. 2—Port Kennedy Cave, Penn. 
1—Afton Junction, Iowa.—Ilst in- 
terglacial stage. 
Ovibos Zone 
4—Alaska Ground Ice. 
3—Conard Fissure, Ark. 
2—Seattered middle west. 
1—Big Bone Lick, Ken. 
