PLEISTOCENE HISTORY OF THE GENESEE VALLEY 

 IN THE PORTAGE DISTRICT 



EY 



HERMAN L. FAIRCHILD 



Evolution of western New York drainage 



Any adequate discussion of the preglacial history of the Genesee 

 river in its broader relations would involve the whole problem of the 

 changes and adjustment in the drainage of the area of western and 

 central New York and northern Pennsylvania during all time since 

 the later Paleozoic. This is a large problem which has not been 

 seriously attacked and one which requires much study. For the 

 purpose of the present writing we shall be content with the briefest 

 presentation of the elements of the problem. 



It would seem certain that the primitive and consequent drainage 

 of the western half of the State, along with the northern and western 

 part of Pennsylvania, must have been southward or southwestward 

 when the region was slowly uplifted from the seas as a coastal plain, 

 bordering the old lands of Canada and the Adirondacks. Such 

 elevation probably occurred not later than the Subcarboniferous. 

 Many of our broader valleys, specially those with a southward or 

 southwestward trend, are probably an inheritance from that earliest 

 drainage across the uplifting plain. In the course of time the at- 

 titude, structure and composition of the rock strata, along with the 

 up and down movements of the land, influenced the disposition of 

 the drainage. 



In the Ontario region a great thickness of weak rocks permitted 

 the secondary or subsequent streams having east and west courses, 

 along the strike of the strata, to develop and strengthen at the ex- 

 pense of some of the older and trunk streams. Eventually some 

 of these subsequent streams united to make a great main or trunk 

 stream, flowing either east or west, and so there was developed by 

 atmospheric and stream work the great Ontario depression. With 

 the deepening of the east and west Ontario valley the drainage along 

 the southern side was reversed by streams developing northward 

 flow toward the Ontarian river. In later geologic time probably 



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