FEBRUARY 16, 1912] 
probably did, and even extended into the 
Susitna Valley. 
Deposits of Former Glaciers 
The deposits of this former glaciation 
are not usually extensive among the moun- 
tains, whence they have easily been re- 
moved by subsequent denudation; nor are 
they very notable in most places along the 
coast, for there the greater portion of the 
deposits doubtless lies beneath the sea. 
Only in a few places, as in the foreland 
that skirts the seaward base of the Fair- 
weather Range, is there an extensive area 
of deposit above sea level; elsewhere the 
general scarcity of glacial deposit is usually 
striking. 
In the interior, on the other hand, and 
notably in the Copper River Basin, there is 
a remarkable development of glacial and 
glacio-fluviatile deposit formed during the 
period of glaciation and during its stages 
of advance and of recession, of which the 
present must be considered a part. Here 
one finds the greater number of glacial 
features common to an area of continental 
elaciation—lake and glacial stream de- 
posits, loess, till, eskers, kames, moraines, 
and marginal channels are found in per- 
fect development over a wide area. One 
familiar with glacial deposits in Kurope or 
America finds himself quite at home in the 
Copper River Basin. 
The Period of Expansion 
There has not been enough study of the 
glacial deposits to render it possible to 
state whether the history of the glaciation 
in Alaska presents the same complexity as 
that observed in Europe and eastern Amer- 
ica; nor can it even be assumed that the 
Alaskan glaciation was contemporaneous 
with the glaciation of these lands. Yet, al- 
though very extensive glaciers still exist in 
Alaska, and although these are certainly 
SCIENCE 
257 
the descendants of the former expanded 
glaciers, it is entirely possible that the time 
since the maximum expansion is as great 
as that in other northern lands, such as 
Norway and Scotland. I can see no no- 
ticeable difference either in the extent of 
post-glacial denudation, or in the weather- 
ing of glacial deposits in Alaska and the 
Alps, or Norway, or Scotland. The great- 
est expansion of Alaskan glaciers certainly 
occurred many centuries ago, and may well 
have been as long ago as the time when the 
glaciers of the Alps shrank back into the 
mountain valleys. The vast work per- 
formed by glacial erosion in the Alaskan 
fiords clearly proves that the period of ex- 
pansion of glaciers was of long duration. 
Difference in Extent of Recession 
There is one very puzzling condition that 
renders the solution of the problem of the 
time of maximum expansion difficult to 
solve. In southeastern Alaska and in 
Prince William Sound the tidal glacier 
fronts now lie from 75 to 100 miles farther 
back than they were in the period of great- 
est expansion, and vast areas of land and 
water have been uncovered by the recession 
of the glaciers. So also there has been a 
very large area uncovered by glacier reces- 
sion in interior Alaska. But in the coastal 
area between Cross Sound and Prince 
William Sound, the glaciers of to-day ap- 
pear to be only slightly less extensive than 
they were at the maximum. According to 
G. C. Martin,2” the present surface of Martin 
River Glacier is only 600 or 700 feet lower 
than during the maximum glaciation, while 
Bering Glacier is only about 200 feet 
lower; and the horizontal extension of the 
glaciers at the period of maximum expan- 
sion was only very slightly beyond the 
“Martin, G. C., ‘‘Geology and Mineral Re- 
sources of the Controller Bay Region, Alaska,’’ 
Bull. No. 375, U. S. Geol. Survey, 1908, pp. 50-52. 
