PLEISTOCENE HISTORY OF THE GENESEE VALLEY " 79 



While the ice was resting against the salient at Batavia it receded 

 from the bills south and west of Syracuse permitting the impounded 

 glacial waters to escape eastward, a direction of outflow contrary to 

 the former stage. The waters are named for Lardner Vanuxem, 

 whose district in the early Geological Survey of New York com- 

 prised the central portion of the State. 



The higher terraces on the delta either side of the canyon at 

 Mount Morris, at 840, 800 and 740, may have been made during 

 this stage; also the deposits about the mouth of the Keshequa, and 

 the lower terraces east of Bishop Corners, at 825 and 750. 



St Helena- Gibsonville morainal lake. When the waters fell 

 below 900 feet on the Mount Morris parallel the valley above the 

 " High Banks " was left holding a local lake, which we name as 

 given above. In preglacial time this valley probably opened to the 

 south [see p. 73] as the walls at the north are rock. The lake may 

 be called morainal, however, since the south end was blocked by the 

 Portage moraine. 



The St Helena-Gibsonville morainal lake (or St Helena lake for 

 brevity) was contemporaneous with the Lake Vanuxem and later 

 waters. The initial height of the lake is definitely shown by the 

 broad gravel plain, coinciding with the top of the rock, at the " High 

 Banks" at 900 feet; and the extensive delta plateau opposite the 

 Silver lake outlet also at 900 feet. All terraces in the St Helena 

 Valley below 900 feet must belong to the local lake and correlate 

 with the downcutting of the Mount Morris canyon. 



As the crest of the lower Portage falls is only 850 feet in altitude 

 they could not have been initiated until the " High Banks " outlet 

 and St. Helena lake was lowered to that level. 



Tuscarora morainal lake. With the falling of the waters in the 

 Dansville valley below 800 feet a local morainal lake was left in 

 the lower or northern part of the Nunda valley, due to the drift 

 blockade south of Sonyea. This local water did not reach as far as 

 Nunda but covered the site of Tuscarora. 



The point of lowest escape was north of the moraine, and north 

 of the ancient valley. Failing on the rock the outlet was compelled 

 to cut the shallow canyon, about 100 feet deep, southwest of Sonyea 

 now occupied by the Keshequa creek and utilized by the railroad. 

 During stages 9 to 12 the cutting must have proceeded, but with 

 interruptions as the base level waters in the Dansville valley changed 

 their level. 



