426 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1944 
date, of course, but they do furnish a basis for making estimates. This 
will be considered in more detail in connection with the discussion of 
the ages which have been assigned to all such finds. 
SUMMARY AND DISCUSSION 
It is evident, from the manifestations discussed in preceding pages, 
that man had reached the New World when large portions of North 
America were still covered by remnants of the Wisconsin ice sheet. 
The physical characteristics of such remains as have been found, as 
well as those of the later Indians, indicate an Asiatic origin and subse- 
quent migration. This spread probably did not take place as a single 
mass movement but as a series of continuing migrations by relatively 
small bodies of people over a long period of time. When this began 
and the routes followed are matters about which opinions differ. Most 
students of the problem, however, agree that the bulk of the aboriginal 
population arrived by way of the Bering Strait region and from there 
gradually spread over North America, through Middle America, and 
into the southern continent. The great central plain in Alaska and 
the lowlands bordering Bering Sea and the Arctic Coast were not 
glaciated during the last stage of the Pleistocene. Moreover, there 
was an open corridor along the eastern slopes of the Rocky Mountains 
in the period just after the climax of the Wisconsin. As a consequence 
it was possible for men and animals to pass from central Asia to the 
tip of Siberia and across to Alaska, eastward to the Mackenzie River 
and thence southward into the northern plains. Another route by 
way of the upper Yukon and its tributaries, the Liard and Peace 
River valleys, opened subsequently, and not long after this still another 
became available. It led south along the Fraser River, between the 
Rockies and the Coast Range, and into the Great Basin. The presence 
of artifacts, old camp sites, and bones from extinct species of animals 
found in various places demonstrates that full advantage was taken 
of these several natural highways. 
The first migrants were hunters and they undoubtedly traveled in 
small groups. According to present evidence they followed two main 
lines of dispersal, one along the eastern slopes of the Rockies, some 
continuing on south toward northeastern Mexico, and others spread- 
ing out over the plains to the more southerly reaches of the Mississippi 
River and from there to eastern portions of the country. It may be 
pure coincidence, but it is interesting to note in passing that the 
northern boundary of the distribution of sites attributable to these 
people approximates the line of moraines left by the retreating glaciers 
following the climax of the last Wisconsin substage. The other 
movement seems to have been along the plateau between the Rockies 
and the Coast Range into the Great Basin, southern California, 
