30 NEW YORK STATE MUSEUM- 



lesser tongue pushing up the Mohawk gorge and a larger lobation 

 in the low ground to the southwest. The ice seems to have pressed 

 against the slope west of South Schenectady while it weakened 

 northward and opened the 600 feet gap between the two hills near 

 the Mohawk, in such manner that the col at the head of the Plotter 

 and Poentic kills was not subjected to stream cutting. 



The detritus carried by the higher flow across the Rotterdam 

 salient must have been swept on in confined waters, around the ice 

 lobation, through Altamqnt and southward to quiet waters in the 

 Hudson valley. The detritus of the later flow seems to have con- 

 tributed to the sand plains about South Schenectady, with altitude 

 of 340 feet. 



The south wall of the Mohawk at Rotterdam Junction may have 

 been undercut and steepened by glacial flow crowded against the 

 slope. 



Area and sand plains. Plate 15 shows the hypothetic extent of 

 the lake as mapped for its middle phase. On account of its lower 

 altitude the Amsterdam waters formed only a relatively narrow 

 body in the Mohawk and Schoharie valleys, especially for the later 

 phase. In the Rome district the waters spread more widely along 

 the receding Ontarian ice ; north of Fonda and Amsterdam they 

 reached so as to flood the Sacandaga and upper Hudson valleys, 

 as long as the lake stood over about 760 feet, below which the 

 Sacandaga held a tributary lake (see page 35). 



Allowing for deformation the higher plane of the waters in the 

 district of the Lansing kill and upper Mohawk should be 70 feet over 

 the Schenectady outlet, or up to about 900 feet. On the parallel 

 of Rome the uplift is 60 feet and the latest plane would be about 

 420 feet. 



The delta plains built in the Amsterdam waters by tributary 

 drainage occur widely distributed over the basin and agree with 

 the theoretic levels. The most massive deposits are naturally found 

 at the debouchment of the heavy streams. On West Canada creek, 

 south of Trenton village, the sand plains are from 880 down to 

 740 feet, being partly contributed by drainage from the Lansing 

 kill lake. On East Canada creek, south of Dolgeville, the plains are 

 from 800 feet down. At Johnstown are water levels at about 700 

 feet. Li the Sacandaga valley are excellent terraces and extensive 

 plains, shown in plate 8. North of the village of Northville is a 

 fine plain at 860 feet. The plains of Northville and of Sacandaga 

 Park are 800 feet. The higher levels of the broad plains south of 

 Northville extending five miles to the Great Vly, declining from 800 



