GLACIAL GEOLOGY OF THE SCHENECTADY QUADRANGLE 



MODIFICATIONS OF ROCK TOPOGRAPHY PRODUCED 

 DURING THE PLEISTOCENE PERIOD 



GENERAL ICE EROSION 



The yielding nature of the shales and argillaceous sandstones was 

 favorable to extensive abrasion by the moving ice sheet. The extent 

 to which the rock surfaces were generally modified by this cause 

 can not well be determined, but in some localities evidences of ice 

 erosion are conspicuous. 



In the Glenville hills region there are many terracelike stretches 

 with bedrock of sandstone or shaly sandstone, detached fragments 

 of which are scattered on the surface. It is inferred that these frag- 

 ments of rock were produced by the process of plucking, or loosen- 

 ing of joint blocks by moving ice. The leveled surfaces may have 

 resulted from the more ready removal, by ice abrasion, of the less 

 resistant shales that are interstratilfied with the layers of sandstone. 



In the same region there is a valley which is judged to have orig- 

 inated by ice erosion. It is indicated by the contour lines of the 

 sheet and lies a short distance west of the road which runs south- 

 westerly at a distance of about one and a half miles east of Town 

 House Corners. The valley is in the form of a narrow troughlike 

 depression about one and a half miles in length and five or six hun- 

 dred feet in diameter. It is excavated in the bedrock ; outcrops of 

 shaly sandstone, horizontal in position, show on both slopes. In 

 cross section the valley is U-shaped and its depth, taken near the 

 middle portion, is estimated at 40 feet. The valley opens at its 

 southern end in the general depression of the ]\Iohawk channel. 

 The bottom is not occupied by a stream and there is a divide in the 

 middle portion which seems to render improbable the view that the 

 valley as a whole is of stream origin. The slopes are clean-cut, 

 evenly rounded and closely parallel. No glacial scratches were 

 found in the vicinity but the direction of the valley coincides well 

 with that of the striae found elsewhere. 



GLACIAL SCRATCHES 



In general the bedrock where exposed is worn and broken at the 

 surface, because of weathering. In considerable portions of the 

 area, therefore, glacial scratches are infrequent or lacking. They 

 have been observed in the following localities : 



I North of the city of Schenectady on surfaces of sandstone in 



