14 NEW YORK STATE MUSEUM 



SURFACE DEPOSITS 

 Having noticed the more general topographic features of the area 

 as determined by the underlying rock surfaces and the modifications 

 of these features by erosion during the glacial period, we may de- 

 scribe the deposits or surface materials of Pleistocene age. 



UNMODIFIED TILL 



By this is meant the materials derived from the ice sheet, whether 

 left from the bottom or dropped from the ice at the time of melting, 

 which have undergone little or no disturbance since they were 

 originally deposited. They are distributed generally over the up- 

 land regions of the area and in smaller patches, at lower levels, 

 where the land rose above the surface of the waters of the flooded 

 epoch. About one-half of the surface of the Schenectady sheet is 

 covered by till. 



The thickness of the till varies from a few inches to upwards of 

 a hundred feet. As far as observed the thickest deposits lie in the 

 hills southeast of the Mohawk gorge below Aqueduct. Borings made 

 for water near the residence of Mr W. T. Hanson, near the station 

 Knolls on the Troy branch of the New York Central Railroad, pene- 

 trated 130 feet of . earthy materials before striking bedrock. A sec- 

 tion of the till at this place is afforded by the grading of a roadway 

 running from the base of the hill, where bedrock is exposed, to the 

 summit. It consists in the lower portion largely of compact dark 

 clay, inclosing large and small boulders and without appearance of 

 stratification. Higher up the mass is of looser texture and the rela- 

 tive amount of sand is greater. 



A fine exposure of till may be seen near the point where the 

 macadamized road running east of Round lake crosses the eastern 

 margin of the sheet. The materials here are of the typically hetero- 

 geneous character and include pockets of evenly stratified coarse 

 sands and gravels, mostly in cross-bedded arrangement, indicating 

 turbulent and shifting local currents. A thickness of about 80 feet 

 is exposed. 



In the Glenville hills region and in the floor of the basin adjacent 

 to these hills the till is generally of sHght thickness. To a large 

 extent the streams have worn their channels to bedrock and there 

 are frequent exposures of rock in the roadside gutters. In the 

 fields fragments of detached sandstone rock are widely scattered. 

 A broad area of thinly covered rocks extends southerly from the 



