GLACIAL GEOLOGY Of THE COHOES QUADRANGLE 39 



RECENT DEPOSITS 



The deposits representing the recent period of geological history, 

 or epoch that has elapsed since the final subsidence and disappear- 

 ance of glacial waters, are (i) wind-blown sands, (2) stream allu- 

 vium and (3) vegetable debris or peaty accumulations in swamps. 



Wind-blown sands. In the western and northwestern parts 

 of the quadrangle there are extensive areas of country thickly 

 mantled with loose sands. These sand fields are the eastern por- 

 tions of a broad belt of sands that extends southwest from the 

 region of Saratoga lake to the Mohawk river. To a large extent 

 the sand is heaped in dunes, although, along the eastern margins 

 of the tracts, there are stretches of nearly level country where the 

 sand has been distributed somewhat evenly over the underlying 

 till or lacustrine deposits. iMany of the dunes are of live sand 

 and show evidence of constantly changing size and position. They 

 exhibit no general uniformity of shape but in individual cases it 

 may be observed that their present growth is toward the form of, 

 a ridge with axis corresponding to the direction of the prevailing 

 strong winds. 



For the most part these sand tracts, especially the one extending 

 southward from Saratoga lake, are uncultivated. Only the marginal 

 portions of the areas where the depth of sand is not great are of 

 any important agricultural value. The native vegetation consists 

 of coarse grasses and of trees — pines, white birches and occasional 

 oaks and maples. These trees are of second growth and are mostly 

 undersized and often of stunted character. 



The source of these blown sands is undoubtedly from deposits 

 originally made in Lake Albany. To the westward from the sand 

 fields south of Saratoga lake there is a nearly 'level plain (the 

 Malta plain, Schenectady sheet) which bears evidence of having 

 undergone denudation. The inference seems warranted that much 

 of the sand of this field has been transported by the winds from 

 the area of this plain to its present location. There is a similar 

 relation between the sand region north of Crescent and a leveled 

 tract to the west on the area of the Schenectady quadrangle. It 

 is, of course, also to be considered that the prevailing strong winds 

 of this general region are west or northwest. 



There are two areas of wind-blown sands with well-developed 

 dunes on the surface of the Hoosic delta deposits. Both of them 

 lie near the eastern border of the delta region and are evidently 

 composed of fine sands that have been sorted from the delta 



