ANCIENT WATER LEVELS OP CHAMPLAIN-IIUDSON VALLEYS 239 



riaiditv in the movement of the crust from New York to Montreal, 

 when the sea was at the upper marine limit in the Champlain 

 country the site of New York city must have been about 650 feet 

 above sea level. If now the rate of depression which has brought 

 about the change of level at New York postulated by this view 

 be assumed to have been in the long run 2 feet a cen- 

 tury, it Avill have taken 32,500 years to accomplish the change 

 which has occurred since the sea stood at its upper limit in the 

 St Lawrence valley. Such figures mean only that the postglacial 

 epoch or phase for the glaciated portion of the country is to be 

 measured, as Gilbert has stated it, by tens of thousands of years. 



COMPARISON OF NORTHERN AND SOUTHERN MOUTHS OF THE HUDSON- 



CHAMPLAIN DEPRESSION 



The most striking- differences are apparent in the recent geologic 

 history of the lower Hudson valley and the wide open mouth of 

 the Champlain valley. In the northern area there are abundant 

 beaches of strong develiopment attesting the action of powerful 

 waves with a fetch of wind over wide sheets of water, and cer- 

 tainly the lower of these water levels are marine as abundant 

 marine fossils in sands and clays from an altitude of 350 feet 

 down to the level of Lake Champlain testify. The typical glacial 

 topography over the plains below the marine limit is largely 

 smothered by wave action involving cutting and filling. Where 

 moraines or eskers exist, they are incised by the horizontal lines 

 of wave action. More than all this the existence of a broad 

 estuary is attested by the widespread distribution of clays bor- 

 dering Lake Champlain, clays on which in the central areas 

 remote from the old shore lines and sand deltas no newer deposits 

 repose. 



In the southern area including the vicinity of New York city 

 and the wide valley of the Passaic and Hackensack, a relatively 

 low area analogous to that at the northern end of Lake Cham- 

 plain, recognizable. wave lines have not been found, no undoubted 

 marine beach, bar, or cliff is known to exist above the present sea 

 level. The glacial deposits are, except in marshy and swamp 

 areas at the surface without suffusion by clays which ought to be 

 expected if the region had been submerged for any appreciable 

 length of time. A diligent search conducted for certainh^ over 



