GLACIAL GEOLOGY OF THE COHOES QUADRANGLE 



45 



the main course became established in the channel extending south- 

 easterly to the Round Lake inlet of Lake Albany. At a later time, 

 with a further subsidence of the lake waters, the Iroquois-Mohawk 

 eroded out the broad and deep valley now followed by Anthony 

 kill. 



The Hoosic river, unlike the Mohawk, maintained its course 

 across the emerged area of the delta, repeatedly shifting its channel 

 from side to side and thus building a series of terraces. 



The subsidence of the Lake Albany waters took place inter- 

 mittently, as is shown by the distinctly terraced forms of the 



Fig. 10 Sketch map showing Lake Albany and drainage courses on the 

 areas of the Schenectady and Cohoes quadrangles when the lake waters had 

 subsided .to the level represented by the present 240-foot contour 



deposits. With the withdrawal of the waters to the level now 

 represented by the 300-foot contour, or somewhat lower, the outer 

 portions of the lake bottom in which the coarser sediments had 

 been deposited emerged as land surface. Thus originated the 

 present upper terrace of the Hudson valley. 



At the next stage of marked subsidence, when the water had 

 receded to the level represented by the 240-foot contour, or some- 

 what lower, the more even portion of the lake bottom which had 

 been built up by deposition of the finer sediments, emerged as land 

 surface, forming the plain of the lower or brick clay terrace. 



