72 



H. L. FAIRCHILD — ICE EROSION THEORY A FALLACY 



the possibly brackish waters of the Ontario gulf have been rinsed out to 

 form lake Ontario, the latest representative of the series of water bodies 

 in the Laurentian basin. 



Present lakes. — Repetition is unnecessary here of the facts and con- 

 clusions given in the preceding pages. The principal factor in the 

 genesis of the Finger lakes is probably the drift barriers, along with differ- 

 ential northward uplift. The postglacial tilting seems to range from 2 or 

 3 feet per mile in the Seneca valley to 5 feet per mile east of lake Ontario. 

 We do not yet know the changes in land attitude which occurred before 

 and during the Pleistocene. There may be some unrecognized factors 

 in the problem, but the idea of " rock basins " has no firm basis in obser- 

 vation, and ice erosion has had but small effect on the region. It is 

 granted that the valley slopes were rubbed by the ice to a smoother 

 contour; that some minor side valleys may have been obliterated b} r 

 filling ; that it is possible, though not probable, that the ultimate and 

 steep portions of some small side valleys might have been so effaced by 

 the removal of the weathered walls of the main valley as to give a " hung- 

 up " appearance to the tributary valley. 



The following table of altitudes of the central New York valleys and 

 lakes gives the quantitative data bearing on the subject : 



Vertical Relations, in Feet Above Tide, of the Central New York Valleys and Ontario 



Basin 



Height 



above 



sealevel. 



Greatest 



depth of 



lakes. 



Depth of 



lakes below 



sealevel. 



Conesus lake 



Hemlock lake 



Canadice lake 



Honeoye lake. . . . 



Mud creek 



Canandaigua lake 



Flint creek 



Keuka lake 



Seneca lake 



Ontario lake 



Cayuga lake 



Owasco lake 



Skaneateles lake. . 



Otisco lake 



Onondaga creek.. . 

 Butternut creek. . . 

 Limestone creek. , 



818 



896 



1,092 



800 



1,000-900 

 686 



1,000-900 

 709 

 444 



246 



381 

 710 



867 



784 

 600-400 

 900-700 



800 



Shallow. 



86 



86 

 Shallow. 



258 



179 

 618 



738 



435 



177 

 294 

 65? 



175 



492 



54 



