Glacial Geology of Western New York. 531 



saliencies, the rubbing of ridges into dnimlinoid forms, and depositing 

 of drift in the valleys. In general they have had a subduing effect, 

 a smoothing-down and levelling-np action. The greatest effect of 

 these forces was doubtless felt along the north-facing slope, or over 

 the northern quarter of the area. The series of east-and-west 

 escarpments which probably once existed here have been so destroyed 

 that only a few traces remain. The greater glacial lakes were also 

 restricted to this lower ground, and they have completed the levelling 

 process. 



In Pre-Glacial time, as now, the region was low upon the north, 

 and the Hamilton and Portage-Chemung terranes formed a high 

 plateau in the central and southern belts. It seems sure that the 

 present northward drainage is following in general its Pre-Glacial 

 direction, save that over the low northern plain the channels of 

 stream-flow are all new. 



The chief problem of the ancient drainage relates to that south 

 of the present east-and-west divide. This water-parting between 

 Laurentian and south-flowing waters is probably of glacial origin, 

 due to morainal filling of old valleys. A partial study of the 

 problem leads to the belief that the entire area of Western New 

 York, with considerable territory of Northern Pennsylvania, was 

 originally drained to the northward. The Genesee river system, 

 flowing north entirely across the State, is suggestive of the Pre- 

 Glacial condition of river-flow. In this connection it should be 

 noted that the crustal warping of the region has been a relative 

 uplift to the northward in Post-Glacial time, which has discouraged 

 the northward flow.^ 



Ice Invasion. 



Directions of Flow. 



Of the direction of ice-movement during the period of advance 

 and culmination of the glacial sheet, little evidence has been 

 collected in this region. The trend of the terminal moraine, making 

 a re-entrant and nearly right angle at Salamanca, indicates a general 

 movement from the north-east, with a movement from the north- 

 west along the basin of Lake Erie.^ 



The directions of movement of the waning ice-sheet are abun- 

 dantly shown by strias and drumlin ridges. The only portion of 

 the area where the later ice-flow was from north-east to south-west, 

 in general, is in the district between the Genesee and Niagara 

 rivers. East of the Genesee the movement was south and east of 

 south. Over this district the ice seems to have been compelled. 

 to flow in the direction of the deep valleys now holding the 

 " Finger " lakes. In the south-west portion of the State the move- 

 ment was away from the Lake Erie basin, or toward the south-east. 



The comparatively abrupt change in direction in the neighbourhood 

 of Rochester is noteworthy. The direction of striae at Rochester is 



1 A map showing the directions of drainage and the water-partings may be found 

 in Bull. Geol. Soc. Amer., vol. vi, pi. xviii. 



^ See papers by Professor T. C. Chamberlin in the 3rd and 6th Annual Eeports of 

 the United States Geological Survey. 



