GLACIATION OF THE ALASKA RANGE 421 
glacial erratics and glacially sculptured mountain tops show that 
the great Copper River Glacier at that point overrode mountains 
5,690 feet in height. The bed of the glacial valley is here about 
500 feet above: sea-level so that the glacial ice must at one time 
have been at least a mile in thickness.* 
The Susitna Basin Glacier to the westward was continuous with 
that in the Copper River basin and was of a similar order of magni- 
-tude. It filled the broad Susitna lowland and extended southward 
down the Cook Inlet depression. It may even have reached to the 
mouth of the inlet, though this has not yet been determined. 
Some idea of the thickness of this ice sheet may be gained from the 
fact that north of the mouth of Skwentna River the Venlo Hills, 
an isolated group of hills which lie more than 20 miles from the 
Alaska Range, show glacial erosion and have foreign erratic bowlders 
at an elevation of 3,300 feet above sea-level, and the ice probably 
stood several hundred feet higher than the point at which the 
erratics were found. Along the flanks of the main range there is 
evidence that the ice surface reaches elevations of over 4,000 feet. 
The conclusion, therefore, seems unavoidable that at the time of 
greatest ice accumulation all of the area between the crescent 
of the Alaska Range and the Pacific Ocean was so covered with 
glacial ice that only the higher peaks and ridges of the range, and 
of Talkeetna, Chugach, Kenai, and Wrangell Mountains projected 
above its surface. It must be remembered, however, that these 
basins were most favorably situated for large glaciers to accumulate, 
for they were surrounded on all sides by high mountains from which 
a multitude of valley glaciers descended to the lowlands. Only a 
part of the ice originated in the Alaska Range to the north and west. 
The restricted development of the earlier glaciers on the interior 
slope of the Alaska Range as compared with those on the south 
and east slope is even more striking than the difference which exists 
between the present-day glaciers on the opposite sides of the range. 
In considering the northern limit of glaciation as shown on the 
map (Plate I) it is necessary to have in mind the fact that much 
of this region is still unsurveyed and that the writer intends to 
show only in a very general way the borders of the area which the 
tF, H. Moffit, oral communication. 
