250 
eral, and yet it comes from a drainage area 
largely protected by snow and ice against 
those atmospheric agencies which trans- 
form hard rock to fine clay. Can there be 
any doubt but that the glacier which pro- 
tects the rock against the atmospheric agen- 
cies must attack it with equal or even 
greater vigor, in order to obtain this vast 
burden of sediment that the streams bear 
away ?7* 
The Recession of Glaciers in Alaska 
Throughout the world the general state 
of the glaciers is one of recession, with 
local exceptions; and it is as true of Alaska 
as of other regions. In the two regions 
where we have the longest record and the 
most detailed studies—Glacier Bay and 
Yakutat Bay—there have been great reces- 
sions during, the period of observation, the 
continuation of a still greater earlier reces- 
sion during the last century or more. For 
instance, in Yakutat Bay the tidal Nunatak 
Glacier receded at the rate of over 1,000 
feet a year between 1899 and 1906, with a 
total recession of over a mile; and the near- 
by Hidden Glacier, ending on the land, 
receded at about a quarter of this rate. 
Prior to this observed recession, both Hid- 
den and Nunatak glaciers had been so far 
advanced that they united and their com- 
bined front reached about 20 miles farther 
out than the present end of Nunatak Gla- 
cier, and 10 miles beyond the present 
terminus of Hidden Glacier. From this 
advanced position there has been rapid and 
long-continued recession which was in prog- 
ress up to 1906 in Hidden Glacier, and 
up to 1909 in Nunatak Glacier. If the 
observed rate of recent recession of Nuna- 
tak Glacier has been steadily maintained 
throughout the period, it is to be reckoned 
as of about a century duration. 
4 See von Engeln, O. D., Zeitschrift fiir Gletsch- 
erkunde, Band VI., 1911, pp. 138-144. 
SCIENCE 
[N.S. Vou. XX XV. No. 894 
In Glacier Bay the phenomena have been 
closely like those of Yakutat Bay. A long- 
continued recession had been in progress 
when the Muir Glacier was studied by 
Wright in 1886, and by Reid in 1891 and 
1892, when Muir Glacier front was about 
20 miles further inland than it had been 
100 or 150 years before; and Grand Pacific 
Glacier front was about twice that distance 
back of the former terminus. Where ice had 
formerly filled the mountain-walled valley 
to a depth of 3,000 feet, the fiord waters ex- 
tended in 1892. This recession has con- 
tinued since then, being especially note- 
worthy since 1899; and now (1911) both 
the Grand Pacific and the Muir Glacier 
fronts are 9 or 10 miles farther back than 
in 1892, the average recession being at a 
rate of not far from 2,500 feet a year for 
the 19 years; but it is to be noted that the 
rate has not been regular, and that the 
greater part of the recession has occurred 
since 1899. The retreat has continued up 
to 1911 in all the glaciers of Glacier Bay 
with the single exception of Rendu Glacier 
(and a small cascading glacier near it), 
which has recently advanced about a mile 
and a half. Glacier Bay has been enlarged 
no less than 50 square miles by ice reces- 
sion in a period of 19 years. Assuming an 
average thickness of 750 to 1,000 feet, the 
total loss of ice in this period is not less 
than 6 or 8 cubic miles. But to this must 
be added that which has been lost by abla- 
tion from above the present ice surface; 
and this is also an enormous amount, for 
all the outer glacier surfaces, even far back 
from their fronts, are now much lower 
than they were in 1892. 
While these instances are the most stri- 
king of which there are records in Alaska, 
in our own studies Professor Martin and I 
have observed scores of other cases, widely 
separated, where there has been notable re- 
cent recession and where it is still in prog- 
