GLACIAL GEOLOGY OF THE SCHENECTADY QUADRANGLE 35 



carried or pushed along by swift currents of water and which were 

 deposited where the currents entered the static waters of Lake Al- 

 bany. The less coarse materials were carried farther on and de- 

 posited in the order of their fineness. The fine clay and sand sedi- 

 ments were borne far out into the lake, building a great delta, as 

 already described. 



When Lake Albany had subsided to the extent that the Mohawk 

 currents were held within the present boundaries of the basin the 

 deposits were powerfully affected by the increased erosive force of 

 the currents. The surface of the mass of coarse gravels heaped up 

 in the western portion of the basin was swept by the swift currents 

 and the finer constituents were picked up and carried on toward the 

 Aqueduct spillway and (as soon as opened) the Ballston channel 

 outlet. These sediments, however, owing to the damming effect of 

 the Aqueduct barrier, were to a large extent redeposited, especially 

 along the northern slope of the valley, thus giving rise to the coarse 

 sands and fine gravels which constitute the surface materials of a 

 somewhat broad area extending from north of Scotia to Alplaus. 

 At a later date when the gorge at Aqueduct had been cut to the 300 

 foot level, the surface of the coarse gravel bed emerged, forming 

 an island where the highest part of the gravel area northwest of 

 Scotia now appears. This island increased in extent with the fur- 

 ther lowering of the waters and the river thus became divided into 

 two streams, one between the island and the slope of the hills to the 

 north, the other approximately where the present river channel is 

 located. As the northern stream gradually shallowed it began to 

 deposit fine sediments and when finally the river abandoned this 

 channel, the sediments remained as the soil of alluvial character 

 described above. 



DEPOSITS FROM FLOATING ICE 



At the time of its flooded condition, especially in the early stages, 

 the Mohawk waters doubtless transported numerous masses oi 

 floating ice. As these blocks melted, and where they became 

 stranded and subsequently melted, the debris inclosed in them was 

 dropped and added to the deposits already made from the waters. 

 In this way the occasional boulders found buried in sands or min- 

 gled with gravels may be accounted for. Interesting examples' of 

 these are found in several localities. There is evidence that an ice 

 block was stranded a short distance north of Scotia. A kettle hole 

 (shown by a depression contour line on the topographic sheet) has 



