34 NEW YORK STATE MUSEUM 



MOHAWK FLOOD DEPOSITS OF GLACIAL AGE 



The broad basin of the Mohawk, west of Schenectady, is largely 

 filled with deposits of gravel and sand. These deposits appear as 

 the surface materials of the extensive depressed area, north of 

 Scotia, crossed by the trunk-line railways. Farther to the south, 

 along the river, gravels underlie the alluvium, as is shown where, on 

 the shores of the islands, the alluvium has been swept off. The 

 bed of gravel has been cut into by the river near the western edge 

 of the sheet exposing a thickness of about 50 feet. The materials 

 as here exhibited consist of cobbles of considerable size, generally 

 smoothly worn, mixed with coarse sand and clay. The clay, or clay 

 and lime, constituent to some extent acts as a cementing sub- 

 stance and masses of considerable thickness, appearing somewhat 

 stratumlike in arrangement, are of conglomerate composition. Huge 

 fragments of conglomerate have become detached and fallen to the 

 base of the bluff. 



The wells from which the public water supply of the city of Sche- 

 nectady is obtained are excavations in this bed of gravel. They 

 are located just south of the river at a point about one mile west of 

 the western extremity of Van Slyck island. There are three wells, 

 varying in depth from 42 to 44 feet. The deepest one is farthest 

 to the east an ( d is excavated entirely in gravel. The other two pene- 

 trate the bed of gravel and have their bottoms on a compact clay of 

 dark bluish color. 



There is an evident gradation from the coarser gravels in the 

 western portion of the area referred to above to finer gravels and 

 coarse sands farther to the east, passing to sands in the immediate 

 vicinity of Scotia. Northwest of Scotia and extending as far as 

 Alplaus the surface materials are mainly coarse sands and gravels. 



North of the tracks of the New York Central & Hudson River 

 Railroad there is a depression which was evidently at one time a 

 watercourse. The soil here is clayey in composition and is believed 

 to represent a deposit of alluvial origin. Another narrow area of 

 clay of similar composition occurs farther to the east, extending 

 toward Alplaus and bordering the modern river alluvium. In map- 

 ping it was thought best to distinguish between these, although the 

 line of demarkation could be drawn only somewhat arbitrarily. 



The bed of coarse gravels above described lying northwest of 

 Scotia and extending to the edge of the sheet and beyond is inter- 

 preted as a deposit made by the Mohawk in the flooded or 'Iroquois 

 stage of that river. It represents the heavy materials which were 



