PLEISTOCENE HISTORY OF THE GENESEE VALLEY 75 



The junction of the Genesee and Dansville valleys is not so clear 

 and satisfactory as we might expect. The rock exposures restrict 

 the valley width and the Genesee is made apparently a tributary to 

 the Dansville river. But this seems to be the only possible outlet. 



It is probable that the preglacial Genesee river with its full le.igth 

 had not been in its acquired channel a great period of time, or in 

 other words was not a very ancient stream. The river had been 

 produced by the diversion or capture or union of different minor 

 streams, and had only in later time become adjusted to the course 

 in which the glacier found it. The Dansville river was probably 

 the older stream, though possibly smaller in volume. Before the 

 ice sheet interfered with it the Dansville river probably collected 

 the drainage from a large territory on the east of Dansville and 

 south of the western members of the Finger lakes, including the 

 upper Cohocton valley. Some of this drainage was inherited from 

 the earliest time, and probably the valley had become mature while 

 the Genesee was young. The glacial drift cuts off the former upper 

 waters and sends them over southward by the Cohocton river, so 

 that the Dansville stream is today only the Canaseraga creek. The 

 greater maturity of the Dansville-Avon valley was noted by Dr 

 Grabau. 



It must be noted that the present floor of the Dansville-Avon 

 valley is not the bottom of the old river valley, but only the top 

 of the deep filling left by the glacier and the glacial lakes, with 

 some contribution by the present streams. 



Glacial waters and canyon cutting 



The initiation of the postglacial canyons and the history of their 

 cutting is intimately tied in with the glacial lakes held in the valley. 

 The various benches along the new channels of the river and the 

 many terraces and plateaus of sand and gravel can not be under- 

 stood without a knowledge of the lake history of the valley. And 

 this drainage history of the Genesee valley is one of the most re- 

 markable and dramatic stories in geologic literature. 



During- the long time, to be counted as many thousands of years, 

 while the south edge of the ice sheet was slowly receding or backing 

 away, from south to north, across New York State, the waters 

 over the Genesee area were held up to high levels, being forced to 

 overflow east or west. In the successive lowering of the waters by 

 the opening of more northward outlets at least seven great 

 river systems have received (and some of them more than once) 

 the contribution of Genesee waters. In order of time these are 

 as follows: (i) Pine creek-Susquehanna. (2) Allegheny-Ohio- 



