GLACIAL GEOLOGY OF THE SCHENECTADY QUADRANGLE yj 



RECENT DEPOSITS 



The deposits belonging to the recent epoch or period that has 

 elapsed since the final subsidence and disappearance of glacial 

 waters are (i) the alluvium laid down on the flood plains of the 

 Mohawk river and the larger creeks and (2) the wind-blown sands 

 of the sand plain areas. Mention may also be made of the peaty 

 accumulations of swamps, or partially drained areas formerly lakes. 



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STREAM ALLUVIUMS 



The alluvial deposit in the basin west of Schenectady is some- 

 what notable both for areal extent and for thickness. Some four 

 or five square miles of valley lands, including the several large 

 islands in the river, are composed of soils of alluvial origin. It is 

 said that it was the fertility of these soils of the " great flats '' that 

 determined the original settlement of Schenectady. 



The lower portion of the basin is still an area of sedimentation. 

 This is shown not only by the overflow of the river on the flood 

 plain at times (high water), but also by the steady growth of the 

 islands west of the Schenectady-Scotia bridge at their lower (down- 

 stream) ends, and the silting up of the channels between them. It is 

 also interesting to note that two new islands have been formed in 

 recent years farther down the river, about half a mile west of the 

 mouth of Alplaus kill. On the other hand, at the western end of the 

 basin the alluvium is to some extent being swept away by the river 

 currents, as is shown by the fact that the underlying gravel has in 

 places been laid bare. 



Another extensive alluvial deposit made by the Mohawk occurs 

 farther to the east below Vischer Ferry. Here the river, aban- 

 doning the rock-bottomed channel which begins at Aqueduct, enters 

 the territory of Lake Albany deposits. The stream has cut through 

 the sands and clays and swept out a broad basin the floor of which 

 consists mainly of till, overlaid, in the flood-plain area, with alluvium. 



WIND-BLOWN SANDS 



The regions of Lake Albany deposits where the surface materials 

 consist mainly of sand show the eflfects of the drifting and heaping 

 of sands by the winds. Some portions of these areas present a 

 highly distinctive sand-dune toi>ography. This is conspicuously the 

 case in the Schenectady-Albany sand plain. The dunes are for the 



