418 NEW YORK STATE MUSEUM 



condition upward with it to the new level, where it will persist 

 for a considerable time and furnish evidence of a former graded 

 condition at the lower level, as well as that the level has since 

 been uplifted; its altitude above the new grade which the 

 streams reach wiill also give the vertical amount of the uplift 

 for the locality. 



Prepotsdam topography 



During the long existence of the Adirondack region as a land 

 area, it has twice remained at a given level for a sufficient length 

 of time to permit the reduction of almost its entire surface to 

 the graded condition. The first occasion was in Prepostdam 

 times, and the comparatively smooth surface on which that and 

 the succeeding deposits were laid down, as shown on all sides of 

 the region wherever this surface can be seen passing beneath the 

 Paleozoic rocks, is the result. At the beginning of Potsdam time 

 the district seems to have presented the aspect of a low, irregular 

 dome, whose slopes were the gentle ones of the streami grades^ 

 and whose longer axis, or main watershed, extended across the 

 regioni in a southeasterly direction, along a line running from a 

 little north of Watertown to a little south of Albany, and also 

 extended northwesterly into Canada. The streams drained away 

 from it in all directions, but principallyi to' the northeast and 

 south^^^est. This axis does not divide the present Adirondack 

 region into halves, but lies well toward itS! southwestern! border, 

 so that, at the commencement of Potsdam time, the sea was close 

 at hand on the northeast Adirondack margin, but was many miles 

 distant from that on the southwest; consequently the depression 

 carried the one area below sea level, while the other still con- 

 tinued as a land area. This effect was accentuated by the more 

 rapid subsidence on the northeast. Thus the sands, carried down 

 by the streams and washed about by the waves, are now found 

 only oui one side of the district; on the other they did not reach 

 the region, and now lie miles away from Its margin, buried deep 

 under newer deposits. 



The surface covered by the Potsdiam deposits on the north and 

 east sides of the district, is found to be much rougher than that 

 on the southwest, which remained unsubmerged during this time 

 and was not reached by the sea till the following Beekmantown, 

 or Trenton; and it is thought reasonable to suppose that thit» 



