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PRESENT TOPOGRAPHY AND PREGLACIAL DRAINAGE. 185 
valley, several hilltops rise to 1,500 and 1,600 feet. The foothills of the 
Adirondacks come down close to Little Falls, while the Utica shale area 
about Johnstown and Gloversville is reduced to levels of 600 to 800 feet. 
On the south the Catskills grade down to the plateau level of central New 
York, lying south of the Helderberg escarpment, with common altitudes 
of 1,500 to 1,700 feet. An exceptional slope appears at Rotterdam, where 
an altitude of 1,385 feet is attained within a mile and a quarter of the 
valley bottom. One thousand to 1,400 feet are common heights for the 
southern parts of the Fonda and Amsterdam atlas sheets. Geographic 
reasons for town sites abound. Six cities lie upon the short course of the 
stream, and more than that number of large and important towns. A 
ford, waterfall, or open ground at the mouth of a tributary is the usual 
physiographic factor in the history. 
PREGLACIAL DRAINAGE 
CRETACEOUS PENEPLAIN 
Studies of the region are not sufficiently matured for confident asser- 
tion. Besides large tracts to north and south, the Herkimer-Sprakers 
section of the immediate valley is yet unmapped, but considerations have 
developed which seem worthy of statement. Until the district is mapped, 
itis reasonable to assume from much general observation that the plateau 
south of the valley, extending into Pennsylvania, is a part of the uplifted 
and dissected peneplain described by Davis and others for the eastern 
and southern Atlantic region. The structure is the same as in northern 
Pennsylvania, “a peneplain on which successive formations crop out, 
one shingled on the next as we cross the country.” * 
These formations originally extended much farther to the north, ear- 
rying the peneplain to an undetermined distance in that direction. An 
outlier of Potsdam, Calciferous, and Trenton is now found at Wellstown, 
12 miles from the body of these formations, at Northville. The Hamil- 
ton rocks would overreach much of the present course of the riverif car- 
ried northward for an equal distance from their present outcrop, and the 
same may be said with stronger emphasis for the Helderberg series of 
limestones. Into the northern edge of the great peneplain, the Mohawk 
valley was cut by prolonged erosion. 
COURSE OF ADJUSTMENT 
It is assumed that the ancient constructional streams led from the 
Adirondacks south and southwestward across New York into the Penn- 
*W. M. Davis: The geological dates of origin of certain topographic forms on the Atlantic slope 
of the United States. Bull, Geol. Soe. Am., vol. 2, p. 560. 
