256 
bergen, whose ends have been rapidly and 
notably pushed forward are apparently il- 
lustrations of the same principle; and be- 
cause of the peculiar nature of the cause 
for the wave, the Yakutat Bay glaciers 
furnish illustrations of an even more spas- 
modiec movement, and a more rapid sub- 
sidence of the wave of advance. There 
are many instances of minor, or minute, 
advances of glacier fronts; and we also 
know of a number of cases of noteworthy 
advances in Alaska and elsewhere. The 
more notable advances seem to be illustra- 
tions of the same principle, that a wave of 
advance, concentrated on the terminus of the 
glacier, pushes it far forward; then follows 
a relative deficiency of supply and conse- 
quent retreat. In the recently advanced 
glaciers of the Yakutat Bay region the sub- 
sequent deficiency has been so great that 
stagnation has immediately followed ad- 
vance. 
We have not yet large enough body of 
fact to warrant the statement of a law, but 
such knowledge as we possess indicates that 
there is reason to expect relatively rapid 
recession following an advance, because a 
deficiency of supply follows as a necessary 
result of the utilization of a part of the ice 
supply in the progress of the wave of ad- 
vance. In other words, the reservoir is 
temporarily depleted by the drain upon it 
during the advance. 
ForMER GLACIATION 
The major part of this address has been 
devoted to the existing glaciers and their 
recent history, for this has been the field 
of my most extensive study. But little 
time remains for a consideration of the 
former glaciation, and what is said must of 
necessity be brief, and must deal with only 
the most general and fundamental points. 
SCIENCE 
[N.S. Von. XXXV. No. 894 
Extent of Former Glaciers 
It is now a well-known fact that in recent 
geologic time there has been a very notable 
expansion of Alaskan glaciers both along 
the coast and in the interior. The fiords of 
southeastern Alaska were filled with ice to 
their seaward entrances, and the same was 
true as far west as the Alaska Peninsula. 
Thus there was a vastly greater ice-covered 
area on the seaward side of the coastal 
mountains than now exists there. In the 
interior there was also notable expansion 
on the inner side of the coastal mountains, 
on both sides of the Wrangell and Alaska 
ranges, and in the Endicott Mountains. 
Elsewhere in the mountains of the interior, 
even where now there are no living gla- 
ciers, there were valley tongues, and per- 
haps even expanded piedmont bulbs. All 
this glaciation was, however, purely of the 
mountain type, and far the greater part of 
Alaska was untouched by it. 
Along the coast there were extensive 
piedmont glaciers, and there were vast 
piedmont ice sheets filling the fiords to a 
depth of several thousand feet, overflowing 
the low islands and peninsulas now sepa- 
rating them, and discharging icebergs into 
the ocean. Piedmont glaciers also de- 
veloped along the inner face of the coastal 
mountains and on both sides of the 
Wrangell Mountains, and the Alaska 
Range. 
By far the greatest area of ice in the in- 
terior was that which, in its maximum 
stage, nearly or quite filled the great basin 
that lies between the coastal mountains, 
the Wrangell Mountains and the Alaska 
Range, forming a great intermont glacier 
by the junction of a series of piedmont 
glaciers. The exact extent and the char- 
acteristics of this glacier are not yet deter- 
mined; and it is not certain that it filled 
the entire Copper River Basin, though it 
