GLACIAL GEOLOGY OF THE COHOES OUADRANGLE 



43 



materials were carried farther and laid down in the quiet waters 

 lateral to the dwindling end of the ice lobe. As a general result 

 of this sorting of the sediments, the materials deposited on the 

 floor of the upper and outer portion of the preglacial valley of the 

 Hudson are coarser (sands and clays of the upper terrace) than 

 those which form the filling of the inner portion of the valley 

 (brick clays of the lower terrace). The latter were added to, how- 

 ever, at a later time, by depositions of fine sediments from the 

 midcurrents of Lake Albany. 



Fig. 8 Sketch map showing the distribution o£ land and water on the 

 areas of the Schenectady and Cohoes quadrangles when Lake Albany was 

 at the height of its development, its level corresponding to the present 360- 

 foot contour 



When the ice lobe had melted back beyond the northern limit of 

 the quadrangle, all parts of the area the elevation of which is 

 below approximately 360 feet on the northern portion of the present 

 map and 320 feet in the southern were covered by the waters of 

 Lake Albany. The lake waters rose beyond the height of the 

 western marginal boundary of the preglacial rock valley of the 

 Hudson and extended in two broad sheets westerly, communicating 

 with the expanse of Lake Albany that overspread the eastern and 

 southern portion of the area of the Schenectady quadrangle. The 

 body of waters thus developed received the Hoosic river at its 

 eastern border and the flooded Iroquois-Mohawk (then the outlet 



