GLACIAL WATERS IN BLACK AND MOHAWK VALLEYS 2g 



outflow: the upper plains at Prospect and Trenton Falls (1160- 

 980) ; the lower at Devereaux-Stratford (i 160-1000) ; the higher 

 at Northville-Edinburg (1040-940) ; the lower at Poland (940- 

 820) ; and the terraces in the Lansing kill valley and the upper 

 Mohawk at 1200 to 920 feet. 



It will not be possible to discriminate sharply the upper and 

 lower limits of the Schoharie waters, as the Herkimer waters fell 

 slowly to the Schoharie and the latter to the next stage. If either of 

 the changes had occurred suddenly and through a large vertical 

 interval the two stages would be distinct in their deposits. How- 

 ever, within the extreme vertical limits as given above there is a 

 large range of levels which must certainly correlate with the Scho- 

 harie stage. 



The evidences of standing water will not be emphatic on the 

 south side of the INIohawk valley as the steep, short slope, the shale 

 rocks, and the weak streams are unfavorable to production and 

 to preservation of delta deposits. 



■ FOURTH STAGE : AMSTERDAM LAKE 



The outlet channels of this stage are shown in plate 6, and the 

 hypothetical position of the ice front in plate 15. 



During the preceding stage, the Schoharie, the ice must have 

 thrust itself against the high ground west of Schenectady, the 

 Rotterdam salient, so as to block the direct outflow of the Mohawk 

 valley waters by the present Mohawk, and forced the waters around 

 through the Schoharie valley and out by the Knox and Delanson 

 passes. In this third stage the ice front weakened on the Rotterdam 

 salient so as to allow outflow by Rotterdam Junction and South 

 Schenectady. 



Theoretically the stream work of this stage must begin at a level 

 below that of the Delanson channel, or 840 feet. At Pattersonville 

 this plane might be 860 feet. Examination of the locality finds the 

 facts in accord with the philosophy. The face of the hill three miles 

 north of South Schenectady, forming the point of the great triangle 

 between the Mohawk and Normanskill valleys, is strongly terraced 

 and gullied down to 360 feet. The hollow on the northwest side of 

 the hill contains a handsome channel at 580-600 feet. The face of 

 the next hill shows stream work up to about 700 feet. The col be- 

 tween the heads of the Plotter kill and the Poentic kill is occupied 

 by uncut moraine drift. 



The general history of the ice recession in this district seems 

 clear. The ice margin curved around the Rotterdam salient, with a 



