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HYDROLOGY OF NEW YORK 



41 



from 1500 feet to 2000 feet, the northern extremity of which lies 

 in the central part of Wyoming county. To the north of this 

 there are three well-defined terraces gradually stepping down to 

 the level of Lake Ontario, the first of which varies from 1000 to 

 1500 feet above tide ; the second, from 500 to 1000 feet, and the 

 third, between about 250 and 500 feet. Lake Ontario lies at a 

 mean elevation of 247 feet above tidewater. It is by these several 

 successive steps that the northern spurs of the New York plateau 

 gradually run out and merge themselves almost imperceptibly 

 into the flatlands about and in the vicinity of Lake Ontario and 

 the St Lawrence river. The course of the streams of this region 

 has thus been defined by the topography. With the exception of 

 those trubutary to the Allegheny river, their course is generally 

 to the north, to either Lake Erie. Niagara river or Lake Ontario. 



Farther east we find a number of mountain or semimountain 

 ranges which are a part of the great Appalachian system, and 

 which extend across the State in a general course from southwest 

 to northeast. The first of this series extends into New York from 

 Pennsylvania and extends northeast through Broome, Delaware, 

 Otsego, Schoharie. Montgomery and Herkimer counties to the 

 Mohawk valley. This mountain system consists of broad, irregu- 

 lar hills, broken by deep ravines, with many of the slopes steep 

 and precipitous. To the north of that river an elevated area of 

 crystalline rocks forms the Adirondack mountain range, which 

 extends to Lake Champlain. To the westward of this area the 

 land is more level, gradually declining to the northwest until it 

 finally terminates at the level of Lake Ontario and the St Law- 

 rence river. The streams of these sections mostly flow west and 

 northwest to the east end of Lake Ontario and to the St Lawrence 

 river, while a short distance from the Mohawk they flow south to 

 the Susquehanna river. The Chenango river is the typical stream 

 of the section, tributary to the Susquehanna. 



Still farther east and south of the Susquehanna valley a second 

 series of mountains enters New York from Pennsylvania and 

 extends northeast through Sullivan, Ulster and Greene counties, 

 terminating in the Catskill mountains upon the Hudson. The 



