530 Professor Herman Le Roy FaircMld — 



1. Pre-Glacial subaerial erosion, probably effective since the close 

 of the PalEeozoic, and acting upon nearly horizontal strata of varying 

 composition and resistance. 



2. Glacial corrasion and transportation, supplemented both in the 

 advance and retreat of the ice-sheet by the distributing and levelling 

 action of glacial and morainal lakes. 



3. The present brief period of renewed atmospheric and stream 

 erosion. 



The northern one-fourth of the area, forming a belt 25 miles wide 

 along the south shore of Lake Ontario, was more deeply eroded by 

 the Pre-Glacial agencies, as it contained all the limestones and the 

 softer shales. It also suffered the greatest modification by the Glacial 

 and lacustrine forces. It now forms a plain rising from about 300 feet 

 elevation above tide near Lake Ontario to 600-7U0 feet at the distance 

 of 25 miles south. 



Southward the surface of the country rapidly rises into an elevated 

 but irregular plateau, formed of the more enduring arenaceous strata, 

 deeply gashed by stream erosion. The higher remnants of the plateau 

 have an elevation considerably over 2,000 feet. The remarkable 

 series of lakes known as the " Finger Lakes " occupy old stream- 

 valleys along the northern border of this plateau. 



Hydrography. 



The waters of this area contribute to three great river systems. 

 The greater part of the area is drained into the St. Lawrence, chiefly 

 by the Genesee and the Oswego rivers, into Lake Ontario, only 

 a minor tract draining into Lake Erie. The south-west corner of the 

 State is drained by the Alleghany river into the Ohio-Mississippi, 

 while the south-east part of the area is drained by the Susquehanna. 

 The waters of the Mohawk-Hudson and of the Delaware lie beyond 

 our eastern boundary. 



The Genesee river is the only present stream which traverses the 

 whole breadth of the State. Having its origin in Pennsylvania, it 

 carries the line of water-parting between the Laurentian and the 

 south-flowing waters beyond the southern limits of the State, and 

 separates the Ohio-Mississippi and the Susquehanna drainage districts. 



Few lakes occur in the streams of southern drainage. Excepting 

 Chautauqua Lake, in the extreme south-west corner of the State, they 

 are of insignificant size, and are all of glacial or morainal origin, and 

 lie in cols or near the divide. 



The series of large parallel lakes referred to above, lie along the 

 north slope of the high plateau, and occupy ancient, deep river- 

 valleys, whose channels have been partially blocked by drift, and 

 further basined by the northward differential uplift of the region in 

 Post-Glacial time. 



Pre-Glacial Topography and Drainage. 



The glacial and glacio-lacustrine agencies did not, it is believed, 

 materially change the larger features of surface relief. Their effect 

 is seen chiefly upon the minor topography, as a smoothing of 



