248 
temperate climate, wastage by ablation 
would normally be active, and if the ice 
supply failed the glaciers would rapidly 
recede. But the sheet of ablation moraine 
that develops serves as a blanket against 
both melting and evaporation, and the rate 
of wastage so decreases with increase in 
thickness of the morainic cover that there 
finally comes a condition of almost com- 
plete protection. When the moraine cover 
is no longer subject to frequent undermin- 
ing and slumping, vegetation finds a foot- 
hold, and ultimately even a mature forest 
may spread over the moraine that blankets 
the ice. Glacier recession under such con- 
ditions almost ceases and an ice terminus 
may remain for scores of years without 
notable change, even though ice supply is 
completely cut off. 
In view of the fact that a protected ice 
terminus may remain so long in one posi- 
tion, it follows that the piedmont condi- 
tion is not necessarily proof either of re- 
cent expansion or of a continuance of ice 
supply after expansion. Indeed, there is 
reason to believe that the piedmont gla- 
ciers, and the piedmont bulbs of individual 
glaciers in Alaska have been formed by 
expansion at entirely different periods. 
In some the supply is still being main- 
tained and the ice terminus is kept in 
place by the essential balance between sup- 
ply and wastage. This seems clearly to be 
the case in the greater part of the Mala- 
spina Glacier; but elsewhere there is evi- 
dence that the expansion occurred during 
an earlier period of advance, and that the 
ice supply has long since been withheld. 
This is true of the piedmont bulbs of 
Galiano and Lucia glaciers, to the ends of 
which the effects of even a recent notable 
advance did not extend. In still other 
eases, the ends of the bulbs have become 
almost or even completely separated from 
the main glacier by wastage of clear ice 
SCIENCE 
[N.S. Vou. XXXV. No. 894 
areas back of the terminus. The piedmont 
bulb develops during a period of advance; 
it may linger, in more or less mutilated 
condition, through a period of stagnation, 
receiving redevelopment when next an ad- 
vanee of sufficient volume occurs. In other 
words, it does not necessarily represent an 
existing state of activity and supply; for, 
because of the protection of a blanket of 
ablation moraine, it may long retain its 
position even in the face of warmth, abun- 
dant rainfall and failure of ice supply. 
Marginal and Terminal Deposits 
Since on the seaward side of the coastal 
mountains, the ends of so many large gla- 
ciers lie in a temperate, rainy climate, the 
phenomena of terminal and marginal de- 
posit are illustrated with great clearness, 
throwing much light on the origin of sim- 
ilar phenomena in the deposits of former 
continental glaciers. Particularly is this 
true of the piedmont areas, not only be- 
cause of the wide extent of their margins, 
but also because they are existing examples 
of a type of glacier that was formerly com- 
mon in the mountain regions of both 
Europe and America. It can not be made 
a part of this address to consider this sub- 
ject in detail, interesting and important 
thought it is.% Suffice it to say that in 
Alaska one may see in process of develop- 
ment both lateral and terminal moraines 
in great variety of form and composition, 
from stratified gravel or sand, or clay, to 
true till; eskers and kames; outwash 
gravel plains and kettles of various forms 
and sizes; lacustrine deposits of many 
kinds and marginal lakes of various ori- 
gins; marginal channels due to erosion 
™See Tarr, R. S., ‘‘Some Phenomena of the 
Glacier Margins in the Yakutat Bay Region, 
Alaska,’’ Zeitschr. fiir Gletscherkunde, Vol. 3, 
1908, pp. 81-110; also, ‘‘The Yakutat Bay Region, 
Alaska,’’ U. S. Geol. Survey, Professional Paper 
64, 1909. 
