74 NEW YORK STATE MUSEUM 



a little over, are well shown from i to i^ miles east of the mouth 

 of Millington brook, and a perfect sand terrace, fully 200 yards 

 wide, three-quarters of a mile long, and at an altitude of about 

 800 feet, lies against a granite ridge two-thirds of a mile north- 

 east of the mouth of the brook. One-half of a mile above the 

 mouth of Potter brook, and also nearly 2 miles above its mouth, 

 are perfect, small sand terraces at from 800 to 820 feet. At The 

 Glen the railroad passes along the base of a fine flat-topped terrace 

 which rises over 60 feet above the track. It is not shown on the 

 map but by lock level its altitude was found to be a little over 

 800 feet. From i to 2 miles north of The Glen and on the east 

 side of the river there is an extensive sand and gravel flat whose 

 altitude is about 820 feet. 



It is interesting to note that the coarsest deposits are toward 

 the north because there the Hudson river with its load of debris 

 entered the lake. The deposits of this extinct lake also rise gradu- 

 ally toward the north because of the postglacial land tilting. Near 

 The Glen the lake was very narrow. The water of this lake ap- 

 pears to have been ponded by a drift dam across the Hudson river 

 just below the mouth of Millington brook. 



Other extinct lakes. Many other smaller glacial lakes, now 

 either wholly or partly extinct, occur within the map limits. Thus 

 Tripp pond was formerly much larger as shown by a number of 

 fine flat-topped sand terraces lying at from 1020 to 1040 feet. The 

 former lake was over 2 miles long with a drift dam a little over 

 a mile north of the present lake. 



The little valley shown on the map 2 miles southeast of Chester- 

 town is certainly an old lake bottom. Most of the swamp areas 

 are also old lake or pond bottoms. 



Existing lakes. None of the lakes of the quadrangle are of 

 preglacial origin. Some of them, such as Schroon lake, V^alentine 

 pond, Tripp pond, Smith pond, and probably Loon lake, are merely 

 shrunken remnants of former larger bodies of water as already 

 described. The waters of all the lakes and ponds are held in either 

 by glacial drift or old lake deposit dams and most of them show 

 evidence of having been at more or less higher levels. Some of the 

 ponds seem to occupy depressions in the irregularly deposited 

 drift. Ice erosion may have been effective in deepening some of the 

 basins as, for example, that of Friends lake, though positive proof 

 is wholly lacking. 



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