The Idea of Glacial Erosion in America 
203 
the evidence of vigorous erosion in Cayuga valley. “In the 
Finger lake region the ice, moving from the north^vard, after 
entering the valley occupied by Lake Ontario, found its progress 
interfered with by the rising New York-Pennsylvanian plateau. 
Naturally the north-and-south valleys furnished lines of easiest 
escape, and naturally, also, the ice motion was here more power- 
ful and the ice deeper. That the latter was true is proved by the 
fact that, even without the added depth due to ice erosion, these 
valleys were, at the beginning of the glacial invasion, at least 
700 or 800 feet below the general upland level. This increase 
in thickness means, other things being favorable, an increase of 
erosive power. 
Tarr also gives detailed evidence showing the discordance of 
two valleys tributary to Cayuga valley; concerning one of these. 
Six-mile creek, he makes the following statement: “The north- 
and-south valley of Lake Cayuga is several hundred feet below it, 
and its depth has without question been caused by glacial erosion.’’^® 
1894 — w. j. m’gee. 
After listing the characteristics of “glacial canons,” he says* 
“It follows that these features do not necessarily imply extensive 
glacial excavation or indicate that glaciers are superlatively ener- 
getic engines of erosion.”^' 
1898 — H. GANNETT. 
Following a very complete description of glaciation in Lake 
Chelan valley, Gannett thus concludes: “There are therefore 
‘ certain characteristics by which the gorge produced by glacial 
erosion may be distinguished from that produced by aqueous 
erosion. The glacial gorge has the shape of the capital letter U, 
while the water-worn gorge is a V-shaped notch. In a glacial 
gorge the spurs separating the tributaries have their ends blunted 
or planed off, while in a water-worn gorge they are sharp and 
angular. In a glacial gorge the tributaries enter the valley above 
its level, while in a water-worn gorge they commonly grade down 
15 
16 
17 
Bulletin of the Geological Society of America, vol. v, p. 351. 
Ibid., p. 350. 
Journal of Geology, vol. ii, p. 364. 
