70 NEW YORK STATE MUSEUM 



taining a pond) below the level of the plain. Such depressions 

 are thought to be due either to unequal deposition of the delta 

 material or the presence of large buried blocks of ice which on 

 melting would leave the depressions. The contact of the lake sur- 

 face, at its height, with the surrounding land is quite accurately 

 indicated by the 760 foot contour line but, because of postglacial 

 changes of level, the actual altitude of the lake above the sea is not- 

 known. On a line passing east and west through Warrensburg 

 the main body of water showed its greatest width of about 3 miles. 

 Clearly defined sand terraces, the highest of which always rise to 

 the 760 or 780 foot contour lines, prove that important arms of 

 the lake extended fully 9 miles up the Schroon river valley above 

 Warrensburg; nearly 4 miles up the Hudson valley above the 

 mouth of the Schroon ; and at least 2 miles down the Hudson from 

 the mouth of the Schroon. The altitudes of these sand terraces 

 gradually increase slightly toward the north because of the post- 

 glacial warping of the region as explained on page 66. 



In the vicinity of Warrensburg, and especially along the Schroon 

 river, the lake deposits, though deeply trenched, have seldom been 

 cut through to the underlying rock. As a result of the meandering 

 of the Hudson and Schroon rivers, during the process of trench- 

 ing the old lake deposits, fine terraces have been developed. Such 

 terraces are particularly well shown between Potter, Heath, and 

 Moon mountains where, they are at two or three difi^erent levels 

 and from a quarter to a half mile back from the river as the 

 contour lines partly indicate. 



The cause of the standing water was a blockade, probably of 

 glacial drift, in the Stony Creek gorge (Luzerne sheet). 



Glacial Lake Pottersville. This lake, here described for the 

 first time, must take rank as one of the largest and most interest- 

 ing extinct glacial lakes yet recognized in the Adirondacks. It is 

 so named because the best example of sand flat delta deposit 

 formed in the lake lies in the vicinity of Pottersville. This sand 

 plain covers fully a square mile at an altitude of about 800 feet,, 

 though the highest waterlaid sands and gravels occur from one- 

 third to two-thirds of a mile northwest of the village and at an 

 altitude of nearly 900 feet. This material was all formed as a 

 delta deposit by Trout brook in a body of water which stood at 

 a level corresponding approximately to the present 900 foot con- 

 tour line at Pottersville. This body of water was Lake Potters- 

 ville of which Schroon lake is only a shrunken remnant. The: 



