GLACIAL GEOLOGY OF THE SCHENECTADY QUADRANGLE 7 



THE BALLSTON ROCK-CHANNEL 



The name Ballston Channel has been given by Woodworth 1 to 

 the topographic feature described by him as follows : " From near 

 Schenectady an old rock-channel trends north north-eastward by 

 Ballston toward Saratoga." 



In the present account this rock-channel will be limited to the 

 broad troughlike depression, extending from near East Line, in the 

 northern part of the sheet, in a general direction about 20 degrees 

 west of south and joining the Mohawk valley west of Aqueduct. A 

 low divide, at about 300 feet A. T., occurs in the bottom of the 

 trough at about one-third of its length from the southern end. North 

 of this divide lies Ballston lake, a narrow body of water, occupying 

 the deepest portion of the channel. The outlet stream of the 

 lake flows sluggishly northward for a mile and then turning east- 

 ward descends to the Round lake basin, described below. South 

 of the divide the drainage is to the Mohawk river by Alplaus creek 

 which enters the channel from the west through a narrow defile cut 

 into the rocks. The altitude of Ballston lake is 285 feet; the slopes 

 of the channel on either side of the lake rise to upward of 400 feet 

 A. T. The width of the channel taken across the southern end of the 

 lake is a little less than a mile. The floor of the channel, especially 

 its middle portion and on either side of the divide, consists of bare 

 rocks or rocks thinly covered with detritus. Rocks are exposed on 

 both slopes of the channel, especially in the Ballston lake region. 



As stated by Woodworth, 2 this rock-trough has been determined 

 partly by structure. On the slopes at either side the rocks are gen- 

 erally horizontal in position. In the floor of the trough west of 

 the lake, however, there is a line of outcrop following the axis of 

 the channel, where the rocks are nearly vertical in position. This 

 outcrop is best seen near the station Timeson on the trolley line 

 about one and a half miles north of Ballston Lake station. Outcrops 

 of vertical or highly inclined strata parallel with the axis of the 

 trough occur farther to the north. They are well shown near where 

 Mourning kill turns northerly in its course ; and again east of the 

 same stream, along the road, near the northern edge of the map. 



THE ROUND LAKE DEPRESSION 



About four miles east of the Ballston rock-channel there is a 

 large depression, somewhat circular in outline, in the bottom of 



1 Ancient Water Levels, N. Y. State Mus. Bui. 84, 1905, p.75, 76. 



2 Op. cit. p.;6. 



