THE PLEISTOCENE OR GLACIAL PERIOD 919 



intermigration with Eurasia by the northeastern or northwestern 

 routes during the interglacial intervals. A second prominent 

 feature of the faunas was a southern group consisting of gigantic 

 sloths, armadillos, and water-hogs, whose forebears had come from 



Fig. 600. An interpretation of Mastodon americanus by G. M. Gleeson. 

 (From painting in National Museum, Washington.) 



South America a little earlier when the isthmian route was open to 

 land animals. 



The boreal group. As in the Pliocene, the proboscidians domi- 

 nated the fields and forests of mid-latitudes. The mammoth 

 ranged from Mexico northward, reaching Canada and Alaska at 

 times of maximum deglaciation. In Siberia, the mammoth was 

 covered with wool and hair, and was obviously adapted to a cold 

 climate. The mammoth survived the glacial period in America, 

 and its tusks and skeletons are not infrequently found in beds of 

 peat and muck that have accumulated since, in northern United 

 States and Canada. The mastodon also ranged northward into 



