542 ANNUAL REPORT SMITHSONIAN INSTITUTION, 19 3 8 



animals were scarce or absent; consequently, the men must have fol- 

 lowed the game, and the routes of travel must have been more or less 

 the same. 



A complicating ramification in the study of the problem is that of 

 the glaciation and extent of the ice sheets over North America. Many 

 of the mammals that crossed over from Asia during Pleistocene times 

 seemingly came by way of Bering Strait, either over the ice or by 

 means of a land bridge in that vicinity. Some of them came during 

 interglacial stages, others toward the end of the Late Glacial and in 

 the Early Postglacial. The main pathway from the unglaciated 

 area in central Alaska seems to have been east to the Mackenzie and 

 then southeastward along that river and the eastern slopes of the 

 Rocky Mountains into the Plains. This corridor apparently was 

 open for a time prior to the last glacial stage and then became the 

 first land route available when the glaciers began to melt. Subse- 

 quently, a route due south along the Fraser River opened, and the 

 Pacific coast strip also became available for land travel over most of 

 its length. Some of the animals hunted by Folsom men, the mammoth 

 particularly, probably penetrated into the area in interglacial times, 

 because opinion is that elephants and bison were missing in Alaska 

 in Late Glacial and Early Postglacial times, while others undoubtedly 

 migrated with the opening of the cordilleran corridor. Present indi- 

 cations are that it was at the latter stage that the hunters first ven- 

 tured into this vast New World. Many of the animals that served 

 as game were essentially the same as exist today, but as the people 

 moved toward the south they found and killed forms that are now 

 extinct, such as the mammoth, mastodon, some species of bison, the 

 camel, and the ground sloth. Although these extinct forms are con- 

 sidered as Pleistocene mammals, there appears to be no question but 

 that many of them may have lived on into Postglacial times. For 

 this reason the mere association of man-made tools with bones of 

 such creatures does not necessarily indicate a Pleistocene date. Other 

 complications are brought about by the probability that some forms — 

 the mammoth, mastodon and musk-oxen — followed the retreating 

 glaciers and, when found in some of the more northern districts, are 

 not actually as old as those uncovered in southern localities. How- 

 ever, two of the Folsom sites, Folsom and Clovis-Portales, have been 

 placed at the close of the Pleistocene with mention of the possibility 

 that they really belong within that period, and the Lindenmeier site 

 has been assigned to a phase within the Pleistocene on evidence apart 

 from animal remains. For this reason it becomes increasingly clear 

 that the Folsom hunters must have drifted down along the opening 

 corridor not long after the beginning of the glacial retreat. 8 



8 Antevs, 1935 b; Johnston, 1933. 



