70 



THE CHICAGO ACADEMY OF SCIENCES. 



■ 



\ ' V5- 



% 







Fig. 2. 

 Map of North America showing maximum development of the ice sheet 

 and indicating (1, 2, 3, 4, 5) probable areas in which the life of the englaciated 

 territory was preserved during the Ice Age. Willis, Journal of Geologv, XVII, 

 p. 601. 



ing of the fauna over this immense territory. It must also be borne 

 in mind that in the region immediately south of the ice sheet the faunas 

 of several types of country were crowded together — arctic, subarctic, 

 temperate — and as the ice receded, the mirgation northward was in the 

 reverse order of the southward migration, the arctic forms following 



