DISPERSAL OF NORTH AMERICAN BIOTA. 55 



the subject is unfortunately in a very chaotic state little help 

 can come from this source at present. Yet there are certain facts 

 derived from these fossils which are very significant. For ex- 

 ample, the occurrence in Pleistocene times (Hay, '02 ; Hatcher, 

 '02) of such arctic types as the walrus in Virginia and South 

 Carolina along the Atlantic coast, the musk ox in Pennsylvania, 

 West Virginia, Kentucky, Indian Territory and Iowa, and the 

 reindeer in New Jersey, Pennsylvania, Kentucky and Iowa, cer- 

 tainly shows that an arctic climate once reached far to the south. 

 Although limited, this information clearly suggests the general ex- 

 treme southern limit reached by the arctic types during the Ice 

 Age. As the Wisconsin Ice Sheet was not the maximum one in 



> 



southern extension, these arctic types, in their last migration in 

 all probability, did not start from this extreme southern limit, 

 but to the north of it. This gives us an approximate starting 

 point in eastern North America of the Postglacial return of life 

 to the glaciated region. From the Great Plains westward the ice 

 sheet did not extend far to the south in the United States so that 

 the return movement in that region began much farther to the 

 north, near the Canadian boundary. At present, as has been 

 said, paleontological facts do not greatly aid in understanding 

 the early Postglacial northward extension of the biota. But 

 there is another source of information to which we may appeal 

 and that is to the affinities or relationships of the biota south of 

 the ice margin. This makes it necessary to take into account 

 the general conditions of life in North America south of the 



o 



Wisconsin ice margin, and hence to the areas of preservation which 

 must have existed in North America during the Ice Age. 



2. BIOTIC PRESERVES DURING THE ICE AGE. 

 Repeated glaciation had almost sterilized the northern part of 

 the continent. From whence then came the life now occupying 

 that region ? Many of the problems involved in a reply to this 

 question cannot be answered at present, but others may be, in an 

 approximate manner. Much exploration remains to be done in 

 northern Asia before we can hope to answer certain questions 

 on those elements in our fauna and flora which have decided 

 Asiatic affinities. But when we consider the more characteristic 



