436 STEPHEN R. CAPPS 
been continuously deposited since Pleistocene times, it is impossible 
to make a sharp separation between the deposits which are directly 
or indirectly of glacial origin, and those which are now being formed 
by the streams. Glacial waters form such an important element 
in the drainage of both Kuskokwim and Tanana rivers that all the 
deposits of these two great rivers might be considered to be of 
glacio-fluvial origin. On the accompanying map (Plate I) all 
the Quaternary deposits, including morainal material, glacial 
outwash, terrace gravels, and the present stream deposits, are 
mapped in a single pattern, and are indicated only within the area 
which is believed to have been covered by glacial ice. Beyond 
the northern limit of glaciation, as mapped, the broad lowlands 
of both Tanana and Kuskokwim rivers are covered with Quaternary 
deposits which probably attain great thickness. It should be 
remembered that northwest of Mount McKinley the line along 
which the northern limit of glaciation is mapped, and much of the 
area shown as covered with Quaternary deposits, has not been 
critically studied, and the mapping as given here has only a tenta- 
tive value. 
SUMMARY 
The higher portions of the Alaska Range are still in the glacial 
period, the difference between the present glaciation and the 
former more extensive glaciation being one of degree and not of kind. 
The present mountain glaciers are all of the valley-glacier type, no 
large, unbroken ice caps being known. Even at the time of the 
maximum glaciation the higher peaks and ridges probably pro- 
jected above the ice mass, and the mountain glaciers even then 
were valley glaciers. In earlier times the glaciers protruded from 
their mountain valleys and coalesced into piedmont glaciers. On 
the south side of the range these attained great size, filling both 
Copper and Susitna basins and extending southward along the 
valleys of these rivers to the Pacific Ocean, and having a thickness 
measured in thousands of feet. Ice from these basins pushed 
northward across the Alaska Range through Delta and Broad 
passes, and probably also through Mentasta Pass. On the north 
side of the range the former glaciers were also of much greater 
