Gravel Deposits, Muir Glacter.—Russell. 191 
IT made a hasty examination of the gravel deposit beneath the 
ice on the east side of Muir inlet, in 1890, and believe that if I 
can make clear to my readers how similar accumulations of gravel 
and sand are now forming in other portions of southern Alaska, 
we shall be able to come to an agreement as to the history of 
those under consideration. 
THe Lesson. 
About the outer border of the Malaspina glacier and at the foot 
of the Atrevida, Black and Lucia glaciers on the west side of 
Yakutat bay, there are immense ‘‘boulder washers,” as IT have 
been in the habit of calling them, which are being deposited by 
over-loaded, glacial streams and have the essential feature of the 
‘‘alluvial cones” or ‘‘alluvial fans,” so common in arid regions, 
except that the material of which they are composed is in general 
more thoroughly rounded. They are also similar to the subaerial 
portions of the deltas of high-grade streams. 
One of the most characteristic boulder washers observed in 
Alaska, is on the east side of the Atrevida glacier, and has its 
apex at a locality where a creek of turbid water, called Esker 
stream, rushes.out from a tunnel at the foot of a precipice 
of ice about 200 feet high.* The stream flows for two or three 
miles through a deep gorge, having a moraine-covered bluff of 
ice for its right wall for a large part of the way, and a precipi- 
tous mountain slope, loaded with morainal deposits, for its left 
wall. The gorge has been formed by the melting back of the ice 
owing, in a great measure, to the action of the stream which flows 
through it. Many other sub-glacial streams emerge in a similar 
manner at the margins of the glaciers mentioned above. Some of 
these have cut back deep bays or canon-like recesses in the periph- 
ery of the ice; while others have failed to form re-entral angles 
of this character. Whether or not a local recession of the ice- 
front shall follow the emergence of a sub-glacial stream, depends 
on the volume and swiftness of the stream, and on the amount 
and size of the débris that rests on the ice, and as the ice melts, 
falls into the stream. When the stream is strong enough to keep 
its channel open, a deep notch in the ice-front may result; but 
when the débris from the sides and head of the recession is abun- 
dant, and especially when it is of large size, the channel frequently 
*An illustration of the source of this creek is given in National Geo 
graphic Magazine, Vol. 3, 1891, pl. 10. 
