REPORT OF THE DIRECTOR I9II 3I 



highly tilted rock-strata, but there are convincing evidences that it 

 was greatly modified by ice erosion. It was through the gouging 

 action of moving ice with inclosed fragments of rock that the bed 

 of Ballston lake, a long narrow body of water which occupies the 

 lowest portion of the channel, was formed. 



On account of the weathered condition of the underlying shales, 

 where exposed, glacial scratches are infrequent but they were 

 observed in five localities. The directions of the scratches ranged 

 from 22° west of south, about one mile northeast of the city of 

 Schenectady, to 57° west of south at a locality near the western 

 boundary of the sheet. 



It has long been known to geologists that the gorge of the Alohawk 

 beginning at Aqueduct is postglacial in origin. An interesting 

 part of the present w^ork was the determination of the conditions 

 under which the gorge was formed. When Lake Albany was at its 

 greatest development the ^lohawk river discharged into that body of 

 water at about four miles northwest of Schenectady and built a 

 delta out into the lake as referred to above. It was probably at this 

 time that the preglacial channel of the Mohawk was filled up with 

 deposits. When Lake Albany began to subside the delta emerged 

 as land surface and the ]\Iohawk currents became confined within 

 a channel conforming with the present basin near Schenectady. A 

 spillway became established across the rocks below Aqueduct. At 

 the same time the impeded waters, everywhere pressing against the 

 slopes of the basin, gradually forced a passage into the southern 

 end of Ballston channel. These northward moving currents emerged 

 from the channel near East Line, there discharging into Lake 

 Albany. The two outlet streams from the Alohawk basin to Lake 

 Albany were maintained as long as, through erosion, their beds were 

 kept at the same level. This equality of erosive effects was prob- 

 ably determined by the circunistances that the rate of subsidence of 

 Lake Albany was no greater than the rate of lowering of the beds 

 of the two streailis by erosion. At length, however, owing to the 

 greater extent of bed of the Ballston stream, it failed to deepen its 

 channel as rapidly as its rival and its waters were drawn oft* in 

 favor of the Aqueduct course of the Mohawk. 



A beginning was made by Doctor Stoller in mapping the surface 

 deposits of the Saratoga quadrangle. A considerable portion of this 

 area appears to be covered by materials laid down by Lake Albany 

 waters at different stages of their existence. The work will be 

 continued into the following season. 



