128 NEW YORK STATE MUSEUM 



Adirondack Topography 1 



Except for the period during which the Potsdam sandstone and 

 associated sediments were formed, the Adirondacks have been exposed 

 to excessive erosion, in all probability, since Grenville times. While 

 this was going on they experienced the mountain-making epochs in 

 which the Appalachian and Green mountains were formed, which 

 resulted in a general uplift of the region, accompanied by faulting 

 and very slight folding. Among the topographical features produced 

 by the faulting, the Champlain depression may be noted. 



During the time that the region has been a land area it has stood 

 at a comparatively constant level for at least two very long periods, 

 allowing erosion ample time to reduce the area to low altitudes and 

 subdued relief. The land then presented a low dome with its longer 

 axis extending across the country in a northwesterly direction, 

 roughly running from Albany to Watertown and into Canada. It 

 was upon the first level that the Potsdam and subsequent sediments 

 were deposited. The land was uplifted at the close of this period 

 of deposition and subsequently reduced again to a nearly plane 

 surface known as the Cretaceous peneplane. 2 The present erosion 

 is simply destroying what remains of these old levels. The slopes 

 of these two erosional surfaces are not the same. On the west and 

 south of the Adirondacks, the two merge by insensible degrees into 

 each other, 3 while in the east the distinction between the two is 

 clearly perceptible, but still it is possible by careful observation of 

 the sky-line formed by the hills and more distant mountains to 

 imagine in a scientific way remnants of these peneplanes in the Lake 

 Clear region. 



In recent time the area has experienced a gradual uplift. 4 Th's 

 rising or warping is the resultant of the former presence of the great 

 ice sheet that invaded the land from the north. It undoubtedly 

 covered the entire Adirondack region and pushed its way as far south 

 as New York City. The district about Lake Clear was buried undei 

 a load of ice estimated to be some 4000 to 6000 feet in thickness, 

 subjecting the surface to great compression and producing a marked 



1 For a fuller discussion of the topography of the Adirondacks, see H. P. Cush. 

 ing, N. Y. State Mus. Bui. 96, p. 416, et seq. 



2 For spelling " peneplane," see D. W. Johnson, Geog. Rev., v. I, June 1916. 

 E. W. Shaw at the Albany meeting (1916) of the Geological Society of America 

 questioned the age of the " Cretaceous " peneplane, regarding it of later age. 



3 H. P. Cushing, N. Y. State Mus. Bui. 95, p. 426. 



4 H. L. Fairchild, Amer. Geol. Soc. Bui. 27, p. 235-62. 



