ICE-SHEET EROSION IN NEW YORK 57 



Adverse argument from observed phenomena — Origin and basis of ice the- 

 ory. — The suggestion of deep ice erosion as the cause of the Finger Lakes 

 basins was definitely published by Lincoln * in 1892 and in 1894 by 

 Tarr.f The argument is the discordance of the smaller tributary valleys 

 in relation to their north and south trunk valleys. No other evidence 

 of ice erosion has been given, and it is admitted that the broad inter- 

 valley ridges have not been severely eroded, since transverse valleys 

 occur both open and drift-filled, and that the drift is scanty in the wide 

 belt which includes the several lakes. But it is assumed that the drift 

 filling on the north is not sufficient to cause all the ponding of the 

 waters, and that the valleys have been deepened and basined by ice 

 erosion many hundreds of feet. The argument is essentially the same 

 as for deep valley cutting in Norway or Alaska. As the writer views 

 the matter, the advocates of the glacial origin of the Finger lakes should 

 prove that ice did the work, or at least that it is possible for ice to do it, 

 and not leave the proposition resting wholly on assumption. However, 

 the writer will generously undertake to supply an argument that ice 

 could not do the work, followed by positive proof that ice did not do it.J 



Stagnation of lower ice in the deep valleys. — The slopes of the val- 

 leys and of the entire land surface in the region of the Finger lakes is 

 northward, or against the ice-flow. When the district was buried under 

 the larger ice body the flow of the ice must have been chiefly or entirely 

 a flow of the upper layers down the sloping surface of the glacier. The 

 ice in the depths of the larger valleys was probably inert or stagnant, 

 and served as a bridge over which the upper ice traveled. When the 

 ice was at its maximum, reaching the terminal moraine in Pennsylvania, 

 the thickness of the mass over Seneca and Cayuga could hardly have 

 been less than 4,000 or 5,000 feet. The high and irregular land* south 

 and southwest of the valleys was an obstruction to the bottom flow. 

 Another cause of resistance to flow of the deeper ice was due to the very 

 important fact that the general ice movement during the greater expanse 

 of the glacier was decidedly oblique to the valleys. These combined 

 conditions — the depth of ice, the opposition of the land surface, and the 



*D. F. Lincoln in Amer. Jbnr. Sci., vol. xliv, 1892, pp. 290-301. 



f R. S. Tarr in Bull. Geol. Soc. Am., vol. 5, 1894, pp. 339-356. The latter writing contains a bibli- 

 ography on the subject. 



J Since these lines were written Professor Tarr has published an article, "Hanging valleys in 

 the Finger Lake region of central New York," Amer. Geol., vol. xxxiii, May, 1904, pp. 271-291, in 

 which he argues against glacial erosion of Cayuga valley, using some of the facts and arguments 

 presented in this paper. This is a reversal of the opinion expressed in " The Physical Geography 

 of New York State," 1902, p. 180, where he says: "The conclusions stated in my earlier paper 

 have stood the test of much more extended studies, so that after seven years I am even more 

 fully convinced that the two larger lakes owe their depth below the lake surface in large measure 

 to ice erosion, and that they are in the nature of rock basins. Additional facts have been brought 

 to light in support of this theory and none opposed to it." 



