30 NEW YORK STATE MUSEUM 



ward from Schenectady to the Hudson valley, the surface of which 

 forms the sand plain crossed by the New York Central railway 

 between Schenectady and Albany. 



The Lake Albany deposits cover the greater part of the eastern 

 and northeastern portions of the sheet, the materials here represent- 

 ing sediments laid by waters moving in the general valley of the 

 Hudson. An interesting locality is that of the region of Round 

 lake. This lake lies in the middle of a depression, some four square 

 miles in areal extent, the bottom of which is largely strewn with 

 boulders while the slopes consist of the clays and sands of the Lake 

 Albany deposits. The depression is probably a portion of an old 

 rock valley, as interpreted by Woodworth, but its present topo- 

 graphic features are due chiefly to the erosive action of powerful 

 currents of water which, soon after Lake Albany began to subside, 

 swept across this region. These currents were a portion of the 

 Mohawk flood of the Lake Iroquois stage of that river, diverted 

 northward through Ballston channel and thence easterly across the 

 Round lake region. 



The elevation of the undisturbed Lake Albany deposits is about 

 three hundred fifty feet in the locality of Schenectady. In the 

 southeastern portion of the quadrangle the elevation is less but 

 along the eastern border of the sheet, north of the Mohawk river, 

 the deposits rise to a gradually higher level and in the plain east 

 of Malta show an elevation of three hundred eighty feet. 



A glacial lake not hitherto reported is that named Lake Alplaus 

 which occupied the lowest portion of the extensive basin lying be- 

 tween the slope of the Glenville hills on the west and the Charlton 

 hills on the north. The deposits made in this lake have an elevation 

 of four hundred twenty feet. Lake Alplaus resulted from the 

 accumulation of morainic materials at the time of the recession of 

 the ice sheet, forming a barrier behind which glacial waters became 

 ponded. The greater portion of this moraine, especially in the 

 locality southeast of the village of Burnt Hills, exhibits the char- 

 acteristic features of morainic topography. 



In general the uplands portions of the quadrangle above the 

 levels of the lacustrine deposits are covered with unmodified till. 

 Some interesting evidences of extensive ice erosion were observed. 

 Most notable is that of the broadening and deepening of the 

 Ballston channel, a great troughlike depression which extends from 

 near East Line southeasterly to the present Mohawk valley near 

 Aqueduct. This channel is preglacial in origin, following a lin^ of 



