358 
Culver—The Erosive Action of Ice. 
by cascade into the lakes. These are criteria of well recognized 
value; but they do not seem to the writer to possess the diag¬ 
nostic potency with which Mr. Wallace has invested them. 
The same author believes that all existing lakes must have 
been formed at about the same time, and that a recent one, cor¬ 
responding approximately with that of the glacial period. 33 
If we accept earth movement, as the cause of lake basins we 
must explain why these movements took place only in regions 
glaciated. He suggests tliat such movement might possibly re¬ 
sult from the loading with ice. 
But he thinks that if there had been a subsidence of the ice- 
loaded areas the streams flowing out from them would have kept 
pace with the movement and would have cut their beds dewn 
sufficiently to have prevented the formation of lakes. 
He seems here to have overlooked the fact that at that time 
the streams were overloaded with sediment and were not eroding 
at all but on the contrary were filling their valleys. 
Like many of the English writers on this controversy he ig¬ 
nores the patent fact of the blocking up of valleys by glacial 
debris. He is so fully persuaded of the fact that glaciers are 
mighty engines of erosion that he forgets that they not only cut 
down but fill up; and he does not seem to be at all aware of the 
fact that it is far easier to prove the efficacy of ice in this latter 
capacity than in the former. 
The Duke of Argyle 34 considers glaciers incompetent to form 
lake basins and attributes their formation to orographic move¬ 
ments, but concedes some importance to the damming up of val¬ 
leys. 
Professor T. G-. Bonney 35 represents perhaps the other view 
among English writers on this subject. 
He does not believe in ice action as a cause of lake basins. 
He refers to the Caspian and the Dead sea and other similar in¬ 
stances in which ice could have had no hand. 
He thinks the Alps furnish typical results of ice action and 
the sum of their evidence is, the rough places have been made 
33 Nature, vol. 49, pp. 43-78. March 9, 1893. 
34 Nature, vol. 49, p. 389. 
35 Nature, vol. 49, pp.-. 1893. 
