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broad and bounded by rocky slopes rising, on the north side, to the 

 Glenville hills which attain an elevation of upward of 1000 feet and, 

 on the south, to hills of still greater height. This portion of the 

 valley, therefore, exhibits the features characteristic of a river val- 

 ley of mature development. 



The valley further widens toward the east forming a broad basin, 

 filled with a thick mass of gravel and sand, through which the river 

 has cut its way dividing into several streams which unite at the site 

 of the old city of Schenectady. Rocks are exposed only on the 

 northern slope of this basin, its southern boundary being a bluff of 

 clay and sand forming the edge of the great sand plain that stretches 

 southeast from Schenectady to Albany. There is evidence, how- 

 ever, that there is a rocky bluff, buried by the sand and clay de- 

 posits, lying to the south of the surface bluff. The borings made 

 in 1899 by the United States Board of Engineers on Deep Water- 

 ways 1 show that near South Schenectady the bedrock stands at an 

 elevation of 320 feet and that it then abruptly falls off to 210 feet 

 beneath the valley of the Poentic kill, a southern tributary to the 

 Mohawk basin, about three-fourths of a mile to the north, beyond 

 which rock was not reached. How far eastward the rock-bluff ex- 

 tends is not known. The streams which enter the basin from the 

 south flow on clay bottoms, not having cut their beds deep enough to 

 expose rock. Eastward from Schenectady, near the margin of the 

 sand-covered area, rock shows at the level of 340 feet. 



Below Schenectady the valley gradually narrows and rocks out- 

 crop on the slopes on both sides of the river. 



Just east of Aqueduct there is an abrupt change in the features 

 of the valley. Here the flood plain of the river comes to an end 

 and the stream enters a narrow gorge bounded by nearly vertical 

 walls of rock. This portion of the Mohawk valley, as will be more 

 fully explained farther on, has been formed since the melting of the 

 ice of the Glacial period. 



Where the gorge ends near Vischer Ferry the valley again 

 widens, forming a basin, but no rocks are seen on its slope until 

 near Dunsbach Ferry where they appear on both sides of the river. 

 Borings made by the Deep Waterways Survey 2 met with no rock at 

 a depth of 65 feet below the surface of the basin. 



1 Deep Waterways Report, pt i, p. 540, plate 30; House Doc. v. 71, 1900, 

 a O/>. cit. p.522. 



