DAVIS: GLACIAL EROSION. 
313 
sand feet higher than the latter. The stream flowing through Lake 
Canon descends precipitously over a rocky face in order to join 
Lundy Creek. The bottom of the higher canon is about on a level 
with the main lateral moraine in the lower canon. The same series 
of phenomena is repeated where Silver Creek descends over a rocky 
face to join Rush Creek.It might be assumed that the main 
canons had been excavated by glacial action more deeply than the 
lateral branches, owing to the greater eroding power of the glaciers 
which occupied them. This is a simple and natural explanation of 
the conditions observed, and if we admit the great amount of erosion 
usually assumed for ancient glaciers, it must be accepted as an ade¬ 
quate cause for the great strength of the main channels of ice dis¬ 
charge. To the writer .... it appears that the main work of sculp¬ 
turing in the Sierra Nevada .... is to be attributed to water erosion, 
while only minor features .... are to be referred to glacial action. 
With this conclusion in mind, the great inequality in the depth of 
the main glacial troughs and of their lateral branches, is too great a 
work to be ascribed to the erosive power of ice” (’ 89 , 351-352). 
The hanging valleys are therefore left without explicit explana¬ 
tion ; but it appears from other pages of the report that several of 
the deeper canyons, such as Lundy, now head to the west of the 
general line of mountain crest, and it is therefore possible that they 
are examples of retrogressive erosion, both by water and by ice, since 
the elevation of the Sierra Nevada. If this be the case, the hanging 
valleys may be remnants of an ancient west-flowing drainage system, 
now diverted to a more rapid eastward descent. Some such mean¬ 
ing may be behind Russell’s words: “ Many of the valleys of the 
Sierra Nevada .... are in fact relics of a drainage system which ante¬ 
dates the existence of the Sierra as a prominent mountain range ” 
(’ 89 , 348, 350). 
Wallace on Glaciated Valleys , 1893. — One of the most appre¬ 
ciative statements that I have found concerning hanging valleys is 
an article by Wallace on “The Ice Age and its Work,” which 
presents many arguments in favor of the strong erosive power of 
glaciers. Wallace says: “It is evident that ice erosion to some 
extent must have taken place along the whole length of the glacier’s 
course, and that in many cases the result might be simply to deepen 
the valley all along, not quite equally, perhaps, but with no such 
extreme differences as to produce a lake basin.” Then after giving 
much emphasis to the excavation of lake basins near the lower end 
of a large glacier, where the erosive power is deductively argued to 
