GLACIAL GEOLOGY OF THE SCHENECTADY QUADRANGLE 3! 



The flood which coursed northward through the Ballston chan- 

 nel was a part of the Mohawk flood when the stream was the 

 outlet of Lake Iroquois. There were several conditions which 

 determined this diversion of the Mohawk waters into the channel. 



(1) The subsidence of the waters of Lake Albany. When Lake Al- 

 bany was at its fullest development, trie Mohawk discharged into the 

 body of the lake near Schenectady, its waters spreading widely into 

 the lake as shown by the delta deposits previously described. Later 

 when the lake began to subside and the delta emerged as land sur- 

 face the river became gradually confined to the Mohawk channel 

 and flowed in great volume and with high velocity in that portion 

 of the channel which now forms the basin near Schenectady. 



(2) But the preglacial channel of the Mohawk from near Schenec- 

 tady eastward had been rilled by deposits and the waters now cut 

 }ff from the old outlet sought the lowest levels of discharge left 

 open to them under the new conditions. (3) At Aqueduct and east- 

 ward, where the river now occupies a gorge, a barrier of rock then 

 existed. The present elevation of the rock surface on the north 

 side of the river east of Rexford Flats is the same (according to 

 the contour lines) as the elevation of the bluff bounding the 

 Mohawk basin on the south, near Schenectady. This elevation 

 may be taken at 350 feet. The surface slope of the rocks in that 

 region is toward the south and a thick mass of till overlies the rocks 

 south of the river. These conditions show that when Lake Albany 

 had so subsided that the Mohawk waters flowed within the 

 Schenectady basin, an overflow took place across the Aqueduct 

 barrier and a spillway became established there, the waters entering 

 Lake Albany near Vischer Ferry after flowing over the surface 

 of the rocks and for a distance of some three miles. (4) The 

 Aqueduct barrier acted as a dam against a great rush of waters 

 and while the spillway just described was forming, a second place 

 of discharge from the basin had become established. This was 

 through the Ballston channel. 



The southern end of this channel had been filled with sediments 

 deposited in that portion of Lake Albany now indicated by the small 

 sand plain east of East Glenville. The Ballston lake section of the 

 channel had probably remained open! There is no clear evidence 

 that it received Lake Albany deposits at any time. Woodworth, 1 

 as already quoted, has suggested that during the Mohawk delta 

 stage " the ice sheet lay over this region (Ballston lake) while 



Ancient Water Levels. Mus. Bui. 84. 1905. p. 76 



