Gravel Deposits, Muir Glacier.— Russell. 195 
undisturbed gravel and boulder deposit. The Quaternary gla- 
ciers near Mono lake, California, are known to have done the 
same thing, as is plainly recorded in the gravel-lined troughs 
through which they flowed, and which still retain their original 
contour. 
A more careful study of glaciers may show that there is a ratio 
between the grade of an ice stream and its rate of flow, which de- 
termines whether it shall erode or protect its bed, or permit of 
the accumulation of débris beneath the ice. 
The manuscript of this paper was forwarded in turn to Prof. G. 
Frederick Wright, Prof. Harry Fielding Reid and Mr. H. P. 
Cushing for criticism and suggestions. Their contributions to 
the discussion are given below :— 
Conrripution By Pror. G. FREDERICK WRIGHT. 
Mr. Russell having kindly permitted me to read his paper upon “The 
Origin of the Gravel Deposits beneath the Muir Glacier, Alaska,” and 
having asked me to add any suggestions which come to my own mind 
upon the subject, I would say that his explanation of the origin of the 
phenomena seems to me exceedingly probable, and gives great relief to 
my mind. One fact which he has not mentioned which I had recorded 
(see Ice Age, p. 57) seems to agree perfectly with Mr. Russell’s observa- 
tions. On the west side of Muir glacier the gravel deposits which have 
covered the forests, and which are now in part overridden by the glacier, 
rise from 100 feet above sea-level at the southern termination of the de- 
posit, to more than 300 feet in the vicinity of the present ice-front, which 
seems to be exactly in accordance with Mr. Russell’s theory. 
This explanation furnished by Mr. Russell of the perplexing facts in 
Muir Inlet illustrates anew the complicated character of the forces 
in operation during both the advance and the retreat of a great glacier, 
and shows how competent a glacier is to account for most diverse classes 
of facts. With such a cause in the field, we may well hesitate long be- 
fore concluding that we have exhausted its capacity or resorting to un- 
known causes for the explanation of our facts. 
Oberlin, Ohio, Nov. 10, 1891. 
CONTRIBUTION BY PrRor. HARRY FIELDING REID. 
The explanation given by Mr. Russell of the sand and gravel deposits 
on the shores of Muir inlet seems perfectly satisfactory. From Mr. 
Cushing's observations both he and I were convinced that they were 
formed by running water. The gravels in Main valley and in the valley 
of the Dying glacier probably have a similar origin; in these cases, how- 
ever, they sweep quite across the floors of their respective valleys. We 
often questioned whether the deposits on the two shores were ever con- 
nected, without finding any evidence pro or con, 
