194 The American Geologist. March, 1892 
nearly allied to those of arid regions than are the great boulder- 
washers just described, occur at the mouths of high-grade gorges 
which join broad canons, or valleys, but it is not desirable to con- 
sider these at present. 
THE APPLICATION. 
From the very clear description of the gravel deposits beneath 
the Muir glacier given by Mr. Cushing, as well as from my own 
hasty examination of them, Iam inclined to think that they are 
of the same nature as the boulder washer to which attention has 
been directed. In describing the gravels beneath Muir glacier 
Mr. Cushing says :— 
“They were deposited by swift currents. The material is all coarse, 
alternating beds of gravel and sand, the gravel largely predominating, 
and with little or no admixture of clay. Rapid alternations of horizontal 
and cross-bedding characterize them. A considerable number of the 
pebbles in the gravel are derived from the eruptive rocks far to the 
north. They have their edges rounded but are much more angular than 
are stones which have suffered attrition in water for any considerable 
length of time. They have rather the aspect of somewhat water-worn 
glacial pebbles.* 
Other points of close similarity between these gravels and the 
boulder washes now forming, might be cited from the reports of 
Cushing and Wright; but it is better, perhaps, that the reader 
who is interested in this discussion should consult the original 
dlescriptions. 
If we assume that Muir glacier formerly retreated a few miles 
above its present terminus, so as to allow forests to occupy the 
region about the head of Glacier bay, and that from the extremity 
of the retreating glacier a boulder wash was spread out and in- 
vaded the forest, and should the glacier then advance and over- 
ride the deposit of boulders and gravel, we should have an occur- 
rence similar in every way to what is now found at Muir inlet. 
That glaciers of great thickness may overrun unconsolidated 
gravels, without disturbing them, is no longer open to question. 
An occurrence of this nature on a much larger scale than at Muir 
inlet, may be seen along the southern margin of the Malaspina 
glacier, midway between Icy bay and Point Manby, where the sea 
had encroached upon the glacier and for about three miles ex- 
posed a bluff of ice some three hundred feet high, resting on an 
*AMERICAN GEOLOGIST, Vol. 8, p. 219. 
i 
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