146 The American Geologist. September, 1902 
time and conditions of man's first coming to America, as fol- 
lows : 
'Jlie first people in America appear lo have migrated to our con- 
tinent from northern Asia during the early Quaternary time of general 
uplift of northern regions which immediately preceded the Ice age, 
being its principal cause, and which continued through the early and 
probably the greater part of that age. Then, land imdoubtedly ex- 
tended across the present area of the shallow Bering sea. It is not 
improbable, too, that another line of very ancient immigration, coming 
by a similar early Quaternary land communication where now are 
wide tracts of the sea. passed from western Europe by the way of the 
Faroe islands, Iceland, and Greenland, to this continent. The very 
distant and dim antiquity of these migrations, however, will perhaps 
always forbid our looking back with clear and certain view, to trace 
their relative importancL' and their respective contributions to pre- 
historic American industries, traffic, customs, myths, and racial char- 
acters 
An objection against migrations of primitive man to this western 
hemisphere during the Glacial period may be based on the ice-covered 
condition of North America at that time, wholly enveloped by an- ice- 
sheet upon its northern half, northward from the Ohio and Mississippi 
rivers, excepting the greater part of Alaska. If the preglacial and 
early Glacial altitude of the continent had been the same as now, this 
objection w^ould be valid, and we should be obliged to refer these an- 
cient migrations wholly to a time before the accumulation 6f the 
North American ice-sheet, which reached both east and west beyond 
the present coast lines. But the land elevation then, as known by old 
river valleys submerged beneath the sea and by marine shells of lit- 
tora and shallow Avater species dredged at great depths, was 3,000 to 
S.coo feet greater than now. During the epoch of ice accumulation and 
culmination, its boundaries probably failed to reach generally to the 
coast line of that time. Along the sea border, where food sttpplies 
such as savages rely upon are most easily obtained, preglacial and 
Glacial man may have freely advanced on a land margin skirting the 
inland ice, as along the present borders of Greenland. It was only in 
the Champlain epoch, closing the Glacial period, that the ice-burdened 
lands sank to their present altitude or lower , bringing the edges of 
the ice-sheet beneath the encroaching sea. 
Winchell and others have computed or estimated the dura- 
tion of the Postglacial period as 7,000 to 10,000 years, basing 
their estimates on the rates of recession of waterfalls, of weath- 
ering and dissolving of exposed surfaces of limestone, of 
wave erosion and beach gravel accumulation by lakes, and 
of sedimentation by lakes and streams. This measure, sup- 
plied by many independent observers in America and Europe, 
