824 THE JOURNAL OP VGHOLOG YE 
ularly, local changes in the rate of flow, and even local stagnation 
may be produced. 
Stating this principle in the form of a proposition we have: 
The rate of flow of glacier ice, under given conditions, will depend 
on the percentage of débris commingled with it, and be least 
when the percentage is greatest. The nature of the débris, whether 
coarse or fine, smooth or angular, etc., will modify the result, 
but this need not be considered at present. 
I shall attempt to indicate briefly the bearings of this princi- 
ple in explaining certain glacial phenomena. What follows, 
however, is of the nature of suggestions to glacialists, rather than 
an effort to discuss the various problems touched upon. 
Glacial erosion and subglacial deposition.—In the upper portion 
of a mountain valley that has been occupied by a glacier, as 
for example, Bloody Cajion, California,? the grade is frequently 
steep and the rocks intensely glaciated and but lightly covered 
with débris; lower down in the same valley, the grade decreases, 
and the bottom is deeply filled with débris that was deposited 
beneath the former glacier. In such an instance, the rate of flow of 
the former glacier was greatest in the upper portions of its courses 
and decreased down stream. In the upper portions also, the per- 
centage of débris in the basal layer of ice was least and increased 
toward the extremity of the glacier. The swifter current and light 
change of .débris in the upper portion of the glacier would favor 
erosion; while farther down its course a decrease in the rate 
flow, especially of the basal portion, would result both from loss 
of grade and also because of an increase in the percentage of 
contained débris. The débris-charged ice in contact with the 
rocks would be retarded and when the percentage of foreign 
material in it became sufficient would cease to flow. The heavily 
charged and stagnant bottom layer would increase in thickness 
as more débris was brought from up the valley or descended 
through crevasses and moulins in the ice. When the ice finally 
melted the débris accumulated in its basal portion would be left 
as a ground moraine. 
The increase in rate of flow, in the instance above cited, from 
*Kighth Ann, Rep. U.S. Geol. Surv. 1886-7, pp. 337-340. 
