236 H. L. FAIRCHILD PLEISTOCENE UPLIFT OF NEW YORK 



the Ontario basin to be 20° east of north (95), and that Professor Gold- 

 thwait estimated the post-Algonquin deformation of the Great Lakes area 

 as north 22° east (109). The practical agreement of the conclusions of 

 three independent students, covering overlapping areas, although perhaps 

 somewhat different time episodes, is evidence of accuracy that may be 

 accepted in our court of last resort. 



The writer's study of the Iroquois and marine planes in the Ontario- 

 Saint Lawrence area has been handicapped by lack of topographic maps 

 and precise altitudes. Eecently an advance sheet of the Chateaugay 

 quadrangle made possible the precise mapping of the Iroquois and Gilbert 

 Gulf shores on the west side of the northern salient. We now know with 

 fair precision the altitudes on both sides of the Covey Hill promontory. 

 Here the Iroquois beach ends, while the marine beach follows around the 

 salient, running northwest from the Champlain Valley into Canada, and 

 then southwest back into New York past the villages of Chateaugay and 

 Malone. 



The important fact is determined, which seemed theoretically probable, 

 that the land deformation and hence the isobasal lines of the Saint 

 Lawrence-Ontario area are in accord with those of the Champlain-Hudson 

 and western New England. The Adirondack mass and the wide sur- 

 rounding areas seem to have upraised in unity when the total uplift of 

 both glacial and postglacial time is considered. It appears that the 

 land warping during the successive episodes of the ice removal had some- 

 what different directions in the several provinces of the large area, but 

 the combined effect has produced a fair regularity of slope over the entire 

 area. This is shown by the map (plate 10). 



If the low altitude of the land at tbe close of glaciation had any causal 

 relation to the weight of the ice-cap then it would seem to logically fol- 

 low that no uplifting occurred until the ice-body was waning and the 

 glacial load diminished. This implies that the ice-front had receded 

 from its most advanced position before land uplift began, and it appears 

 quite certain from facts to follow that the land uplift at any point was 

 subsequent to the removal of the glacier at that point. It follows, there- 

 fore, that the summit features of the marine shorelines in the Hudson 

 and Connecticut valleys register the total Pleistocene uplift in those 

 areas; and the same must be true of the deep valleys of New England 

 that lie open to the sea. 



It also appears certain that the Hudson and Connecticut valleys could 

 not rise independently of the regions east and west, except by great and 

 conspicuous faulting. It seems theoretically proper to extend the isobasal 

 lines of equal uplift westward across the whole of New York State and 



