The Parallel Drift-Hills of Western Xew Yorh. 2G3 



into the basins of the Cayuga and Seneca, whei'e it swept between 

 sloping walls of rock nearly 2000 feet in height, and we need 

 not be surprised to find the drift in its present position and shape. 



A carious and interesting effect of this change of form in tlie 

 ice as it ajiproached Cayuga and Seneca, is shown in the direc- 

 tion of the drift-hills in the northwestern part of Seneca County, 

 viz. several degrees west of north, as if the lower part of the 

 glacier which fashioned them had been forced by lateral pressure 

 toward the lake valleys. 



It remains to consider the question of how these hills escaped 

 the changes, so commonly incident to the drift, during the melt- 

 ing of the glaciers. 



As the ice had crejit slowly down to the line which now marks 

 its ancient termination, so did it slowly retire at the close of the 

 glacial epoch. Daring its retreat from Pennsylvania to the 

 highlands of Xew York, the water from its melting edge flowed 

 freely away, and often sorted the drift materials, depositing 

 them not unfrequently in a more or less stratified condition. 

 When, however, the highlands were passed, the conditions 

 changed, and a lake was formed whose southern shore was the 

 mountain ridge, Avhile its northern boundary was a wall of ice. 

 Evidences of the southern shore-line are still apjjai-eut in certain 

 ill-defined beaches, which were described by Professor Hall forty 

 years ago, when they were much better marked than now ; and 

 its northwestern boundary is outlined by beaches in the vicinity 

 of Toronto, several hundred feet above the present level of 

 Ontario. 



This lake undoubtedly discharged its waters southward through 

 the valleys in which lie the small lakes of the mountain ridge. 

 During this period, the parallel drift-hills were in deep watei", 

 and hence beyond the reach of deniiding agencies, though they 

 doubtless received the debris of melting icebergs, particularly 

 the large boulders of crystalline rocks which here and there 

 dot the surface, but are not present in the boulder clay. 



As the melting progressed still further, the Mohawk Valley 

 Avas probably opened, and the Avater sank below the line of the 

 lowest pass of the highlands to the south — that of Seneca Tiake, 

 wdiose summit is now about nine hundred feet above sea-level. 

 That the St. Lawrence vallev was still closed with ice, is ren- 



