8 NEW YORK STATE MUSEUM 



GENERAL TOPOGRAPHY 



BY H. P. GUSHING 



ADIRONDACK HIGHLAND 



The surface rocks of the Adirondack highland are ancient 

 crystalHne rocks of Precambric age. The district is one with an 

 inherent tendency to be elevated and to move upward rather than 

 downward, or at least not to participate in the sagging tendency 

 of adjacent territory during times of oscillations in the crust of 

 the earth. Such a region is spoken of as a positive one, to dis- 

 tinguish it from districts of the negative type, whose tendency is 

 to depress. At certain times in the past the margins of the high- 

 land have been sufficiently depressed to pass beneath sea level 

 and become covered by marine deposits. But the central area 

 of the plateau seems never to have been depressed in this manner, 

 or at least not since very early in Precambric time ; since then it 

 has had a continuous existence as a land area. From time to time 

 it has been uplifted and its surface has experienced much erosion. 

 Between the periodic uplifts long ages of stability have intervened. 

 During these stable intervals the surface has been the scene of 

 incessant erosion, chiefly by stream and rain action. The ulti- 

 mate efifect of such prolonged erosion on a stable land area is 

 to wear it down to a comparatively even surface with low altitude. 

 Such an erosion plain is called a peneplain. If a peneplained dis- 

 trict be again uplifted, stream activity is renewed and the whole 

 erosion process again set in motion. 



The Adirondack highland has certainly been peneplained twice 

 during its history, and quite likely more than twice. The earlier 

 of the two peneplains was completed in Precambric time, and it 

 was upon this peneplained surface that the early Paleozoic deposits 

 of northern New York were laid down, about the margins of the 

 Adirondacks. These covered and preserved this old erosion sur- 

 face and portions of it are reappearing at the present-day surface, 

 as the Paleozoic cover is stripped away from it by modern erosion,^ 

 Its comparative evenness is surprising, when the great variation 

 of the rocks composing it in resistance to erosion is considered. 



In considerable part the present Precambric surfaces of the 

 Saratoga quadrangle represent fragments of this old peneplain, 

 though somewhat modified by comparatively modern erosion. This 

 Precambric peneplain was developed over a wide area and is 



1 N. Y. State Mus. Bui. 145, p. 54-60. 



