356 
Culver—The Erosive Action of Ice. 
(Ramsay), I consider unproven. From the direct observations 
of myself and others on the insignificance of glacial agencies, I 
cannot accept the hypothesis. I find it however worth further 
examination. 
”On the other hand, the attributing of cirques, valleys, and 
fjords to glacial action [Tyndall, Helland], I consider as a 
striking failure to appreciate the occurrence of the working of 
different agencies, as erosion, weathering, glacial agencies, fault¬ 
ing, etc. ” 
During the past year (1893) the discussion on the subject of 
■erosion by ice has again become somewhat active especially in 
England. 
So far as can be gathered from journals and reviews the dis¬ 
cussion in England is at present narrowed down to two oppos¬ 
ing views or hypotheses. The one is the Ramsay hypothesis 
practically unchanged, and the other accounts for the lake basins 
by orographic movements. 
Mr. A. R. Wallace 32 is a prominent defender of the Ramsay 
hypothesis. He writes as follows: 
‘ The first essential to lake erosion is a differential action, 
caused locally either by increased thickness of ice, a more open 
and level valley floor, or a more easily eroded rock, or by a com¬ 
bination of these ... In a narrow V-shaped valley the ice 
might rest wholly on the lateral slopes and hardly touch the 
bottom at all. 
“ On a tolerably wide and level valley bottom however, the 
ice would press with its fullest intensity; and its armature of 
densely packed stones and rock fragments would groove and 
grind the rocky floor over every foot of its surface. ” 
In explaining the absence of a large lake in the Dora Balthea 
vahey, where a glacier produced the great moraine of Ivrea op¬ 
posite its outlet into the plains of Italy, and which forms a 
chain of hills fifteen miles long and fifteen hundred feet high, he 
says the most important point is the extreme narrowness of the 
lower part of the valley above Donnas, and again near its en¬ 
trance into the valley of the Po. The effect of this, he says, 
would be that the glacier, probably 2,000 feet thick or more, 
would move more rapidly in its upper layers, carrying out its 
load of stones and debris to form the terminal moraine; while the 
lower strata, choked in the defiles would move very slowly, thus 
producing little erosion. 
32 Fortnightly Review, vol. 60, p. 750 et. seq. Dec. 1893. 
