FEBRUARY 16, 1912] 
and the work of marginal streams in de- 
posit; indeed almost the whole series of 
phenomena which were present along the 
receding margins of the Pleistocene glaciers. 
There are phenomena of recession, of ad- 
vance, and of alternate recession and ad- 
vance in the course of which soil beds and 
plant remains were incorporated between 
distinet sheets of glacial deposits. 
Of all the deposits at present being made 
in association with Alaskan glaciers, those 
made by the glacial streams are by far the 
most prominent. During the summer, tor- 
rents of water issue from the margins of 
the glaciers, and, where the ice is stagnant 
or thin enough for the existence of sub- 
glacial tunnels, from the central portions 
also. These torrents, doubtless esker- 
building beneath the glacier, spread out 
over alluvial fans, or broad outwash 
gravel plains, or long, narrow valley 
trains, which they are upbuilding by the 
extensive deposition that is made neces- 
sary by the overburdened condition of the 
streams on their escape from the ice tun- 
nels. Over such a deposit the streams 
spread in a multitude of anastomosing 
branches, ever shifting in position as they 
agerade their beds in the effort to estab- 
lish a grade sufficient for the transporta- 
tion of the sediment load. Within a few 
miles of the glacier front the slope of the 
agerading streams may average 50 or 60 
feet to the mile, and close by the glacier 
even much more than this. 
So great is the velocity of the glacial 
torrents that good-sized stones are dragged 
along, and one can hear them striking to- 
gether as they roll on down stream. First 
the boulders are dropped, then the gravel, 
then the sand, and with the change in ma- 
terial deposited is an associated change in 
gerade; but throughout their course the 
grade of the glacial streams is commonly 
very steep, for they are normally so charged 
SCIENCE 
249 
with sediment, and much of the sediment 
is so coarse, that it quickly settles in a slow 
current. Schrader says that in its upper 
course the Klutena River has a grade of 
60 feet a mile, then for 28 miles an average 
grade of 22 feet a mile and a velocity of 
14 miles an hour. The Copper River, into 
which it empties, flows with a velocity of 
8 miles an hour. 
The Sediment Supply of the Glacial 
Streams 
In volume, slope and sediment load the 
Alaskan glacier streams are noteworthy. 
During a period of a few months each 
year the drainage of a wide area, locked 
up in the form of snow and ice, is turned 
into torrents of running water which issue 
as full-fledged streams, and even as veri- 
table rivers from near the glacier ends. 
A glacier that is just at the balance be- 
tween supply and melting furnishes to the 
streams only that water which is brought 
down to or near to the ice front; but in a 
glacier that is receding, there is added to 
this supply all that which is melted from 
the ice that is no longer moving forward. 
Therefore, where, as is so often the case in 
Alaska, the glaciers are stagnant or re- 
ceding, the supply of water exceeds the 
normal. 
The impressive volume of sediment, fine 
and coarse, which the glacial streams are 
transporting leads the inquiring mind to 
raise the question as to its origin. Streams 
having their source in the rainfall are not 
often so sediment-laden as the glacial 
streams normally are; indeed, even the ex- 
ceptional land-supplied streams are rarely 
as heavily burdened, even for a few days, 
as the glacial torrents normally are for sev- 
eral months. Particularly is the question 
of the origin of the finer grained sediment 
of interest. It is abnormal in quantity as 
compared with mountain streams in gen- 
