SOME INSTANCES OF MODERATE GLACIAL EROSION 163 



a nearly level bench below the edge of the steepened slope of Cayuga 

 valley, is a point where, if anywhere in the valley, glacial erosion 

 should have been extensive. 



Farther north, between Union Springs and Cayuga, marked 

 decay was revealed in the gypsum beds of one of the quarries; but 

 this has now been removed. It was situated on a level surface near 

 the northern end of the Cayuga trough, at a point where glacial 

 erosion should have been pronounced, and in a soft stratum which 

 ice-erosion would easily wear away. 



At frequent points near the heads of Cayuga and Seneca valleys, 

 notably near Ithaca and Watkins below the edge of the steepened 

 slope, there are pronounced cliffs, often several score yards in length 

 and from 5 to 15 feet in height, with sharp edges and angles whose 

 formation by ice-erosion is inconceivable. Their length and height, 

 as well as the absence of rounded edges, indicate origin by weathering 

 and not by ice-erosion; and that they were not produced after the 

 ice disappeared is proved in a number of cases by the presence of 

 till and moraine banked up against them and partly burying them. 



A system of hanging valleys tributary to both the Cayuga and 

 Seneca troughs ends at about the 900-foot contour, below which the 

 valley slope is decidedly steepened. Down this steepened slope 

 extend old gorges antedating the last ice-advance, and partly buried 

 beneath deposits of the Wisconsin stage. So far as can be seen, the 

 gorge walls are not markedly worn by ice-erosion. It has been 

 proposed as a theory that the steepened slope and great depth of the 

 Cayuga and Seneca valleys are the result of glacial erosion; but that 

 such profound erosion, amounting to at least 845 feet in the Cayuga 

 and 1,500 feet in the Seneca valley, could have been performed with- 

 out erasing these earlier gorges, or at least so modifying them as to 

 give evidence of such erosion, seems inconceivable. 



The evidence in the Cayuga valley is believed to demonstrate 

 that the work of erosion by the Wisconsin ice-sheet above present 

 lake-level was very slight. What occurred below lake-level or during 

 possible earlier ice-advances is not clear; but if this evidence eliminates 

 erosion in the visible part of the valley by the only known ice-advance 

 in this region, as it seems to do, it throws doubt upon the whole 

 hypothesis of ice-erosion for this valley, notwithstanding the remark- 



