38 NEW YORK STATE MUSEUM 



feet. The difference in the surface and composition of the plains 

 above and below the theoretic plane is noticeable. 



Shore lines are not conspicuous on the east side of the valley, 

 but some cliffs are found on the slopes and terraces by the streams. 

 A fair gravel beach occurs one-half of a mile northwest of East 

 Greenbush, at 320 to 325 feet; another at the south end of Grand- 

 view hill with similar height. Along the road from a mile south 

 of Defreesville to near South Troy the .work of the higher waters 

 is quite evident; 330 to 335 feet at Defreesville and rising to about 

 345 feet at South Troy. 



Along both sides of the Hudson north and south of Albany the 

 terracing of the valley walls is plainly shown by the map, and is 

 very striking in the field. The history is clear; accumulation of 

 detritus in the marine estuary at all stages from the highest, level- 

 ing and smoothing at all levels by the subsiding waters (land 

 uplift), with later erosion by modern drainage. 



Schenectady and Cohoes sheets. Besides the profuse estuarine 

 deposits these two quadrangles hold several important special fea- 

 tures. The Cohoes sheet displays in remarkable form the lower 

 terraces on both sides of the river; the extensive delta of the 

 Hoosick river; and a portion of the later filling by the Iromohawk 

 river. The Schenectady sheet exhibits the deserted channels of 

 the diverted Iromohawk, the north-leading one by the present 

 Ballston Lake, and the subsequent one leading east by the Round 

 lake and Anthony kill. A singular feature is the ice-block kettle 

 holding Round lake. 



The Hoosick delta has been described and mapped by Wood- 

 worth (82, plates 10, 24) ; and the Schenectady quadrangle by 

 Stoller (87) ; while the history of the district has been recently 

 described by the present writer, with a large map (93). The 

 summit plains in the Hoosick valley are at Hoosick Junction and 

 North Hoosick at 400 feet. 



The interesting history of the Round lake district may be briefly 

 epitomized as follows: The delta of the great Iromohawk river, 

 the predecessor of the St Lawrence, headed above Schenectady 

 during the time of maximum submergence, and the current flow 

 was to the southeast. When the land uplift began and the estuary 

 waters retired the river was diverted northward through the Ball- 

 ston Lake channel ; then building the sand plains by Saratoga lake. 

 Further uplift with northward tilting eventually diverted the flow 

 eastward through the Round Lake channel. This flow seems to 

 have continued until the land here had lifted 200 feet of its total 

 rise of 380 feet, as indicated by the stream work in the village, 



