OPTNTOXS OF PREVIOUS WRITERS. 347 



has been evolved. There are two opposite schools, one holding that 

 the lake valleys are merely river valleys clogged with drift, the other 

 school that they are river valleys enlarged ver}^ appreciably by glacial 

 erosion. Spencer, Davis. Upham and Wright hold that the former is 

 the case, while Xewberrj^, Carll, Shaler, Johnson and Chamberlin be- 

 lieve in the hypothesis of ice erosion. 



That the basins are not entirely ice worn is proved by the presence of 

 the large number of pregiacial tributaries flowing in all directions. It is 

 not strange that this, taken in connection with the general form of the 

 lake valleys and their resemblance to mature valleys outside of the 

 glacial belt, should have led those who have taken a cursory glance at 

 the region to conclude that the lakes are merel}" drift-dammed rivers. 

 This is the more natural since the pendulum of opinion has of late years 

 been swinging away from the belief in glacial rock basin erosion, as the 

 result of the fact that so few definite instances of this kind of work have 

 been absolutely proved, notwithstanding tliat the theory lias been l^efore 

 us for thirty years. f 



In his article on the Finger lake region Dr Lincolnt says: 



"From considerable examination of th? country included between the four 

 larger lakes, the writer has been led to set a moderate estimate ui)on the amount of 

 drift, and a very high estimate upon the am )unt of erosion in certain parts." 



He states that in the? cliff, which extends for 20 miles south of Aurora 

 on the east side of lake Cayuga, there are undulations, barely disai)pear- 

 ing beneath the surface of the lake, which appear to rei)resent undula- 

 tions in the old surface. He says : ^ 



"If the lake were drained, the })resont mouths of the brooks tiowino; in these 

 l\ollows would be a mile from the main stream which presumably, occupied the 

 axis of the valley. In going this mile they would fall from 300 to 600 feet. . . . 

 The inference from these considerations is that the pregiacial river which has been 

 dt^veloped into Seneca lake must have occupied a level many hundrerls of feet above 

 the present bed of the lake." !| 



After stating that rock was found in Geneva, at the northern end of 

 lake Seneca, at a depth of 240 feet, Dr Lincoln says : ^ 



"A valley three miles wide between existing rock exposures, and 300 feet deeper 

 than the present lake surface, apparently opening to the north, is indicated at 

 Geneva: some of this depth may be ascribed to glacial action." 



* Am. Jour Sci., vol. xliv, 1892, pp. 290-801 ; Di- Lincoln read a paper upon the same subject before 

 the 189.3 meeting of the American Assoc. Adv. Sci., which the author has not seen. See bibliog- 

 rapliy, 



t Ramsaj'.- Quart. Jour. Oeol. Soc, vol. xviii, 1862, p. 185. 



t Am. Jcur. Sci., vol. xliv, 1892, p. 297; 



^Am. Jour. Sci., vol. xliv, 1892, pi 298. 



II Ibid., p. 299, 



^ Ibid., p. 301. 



XLVIII— BuLi,. Geoi-. Soc. Am., Vol. 5, 1893. 



