GLACIAL GEOLOGY OF THE SCHENECTADY QUADRANGLE 4I 



described, sediments borne by currents from the north were de- 

 posited in the lake, forming the clays and sands of the eastern and 

 northern portions of the sheet. There is evidence that a tongue of 

 ice lingered in the depression of the Ballston channel, thus prevent- 

 ing the accumulation of sediments in the northern portion of this 

 depression. 



The time came when Lake Albany waters began to subside 

 The delta southeast of Schenectady emerged as land surface and 

 the Mohawk currents became confined within a channel conforming 

 with the basin near Schenectady. For a time the flooded waters 

 may have found a passage to the east near South Schenectady in 

 the course marked by the present valley of the Poentic kill. But 

 as the divide between Poentic kill and Normans kill is now about 

 350 feet elevation and allowance must be made for postglacial 

 erosion, it is evident that a spillway was found across the rocks 

 below Aqueduct and the flow of the currents was established in this 

 direction. The rush of waters, impeded by the Aqueduct barrier, 

 forced an entrance into Ballston channel, eroding the sands de- 

 posited in that portion of Lake Albany which occupied the southern 

 end of the channel. The northward moving currents emerged from 

 the Ballston channel near East Line, there discharging into Lake 

 Albany. As the lake further subsided the currents established three 

 watercourses : two northerly, initiating the present valleys of 

 Mourning kill and Drummond creek and one southeasterly, 

 initiating the valley of Anthony kill. The current pursuing the last 

 named course eventually swept away the sands and clays in the 

 Round lake locality resulting at length in the present depression in 

 that region. 



The two outlet streams from the Mohawk 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 probably de- 

 termined by the circumstance that the rate of subsidence of Lake 

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

 two streams 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 off in favor of the 

 Aqueduct course of the Mohawk. 



The present conditions of drainage having thus been initiated, 

 the Mohawk gorge below Aqueduct, the Alplaus gorge below High 

 Mills and the gorge of Anthony kill from near East Line to Round 

 Lake have since been developed. Probably the greater part of the 



