REPORT OF THE DIRECTOR I917 131 



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be discussed later. When preexisting stream valleys are dammed 

 and the rivers are forced to take new courses, they often form gorges 

 with steep or vertical walls, the modern stream action not having 

 had sufficient time to widen and smooth them. The Ausable chasm 

 is a familiar example of such an occurrence. 



Glacial Lakes 



With the swing of the climate toward warmer temperatures the 

 melting of the ice exceeded the rate of its advance, with the net result 

 that it gradually withdrew from the region. As the ice sheet became 

 thinner and thinner the mountain peaks poked their heads above 

 the glacier, becoming a series of islands in a sea of ice. Gradually 

 these islands became larger, surrounded by a growing accumulation 

 of water impounded by the ice. These waters found escape over the 

 ice to the south. This process of melting was continued until 

 entire mountain ranges were exposed. 



Soon the rings of ice, which slowly retreated down the slopes of 

 the mountain ranges, formed a huge ring isolating the Adirondack 

 " island " from the rest of the State. This great ice ring prevented 

 normal drainage to the sea and as a consequence many of the low 

 spots within the barrier were flooded by water resulting from the melt- 

 ing ice and rainfall. Many of the valleys, especially those with north- 

 ward slope and drainage, held a succession of lakes whose existence 

 was due to the ice barrier. These glacial lakes have left great sand 

 plains, deltas, terraces, beaches and water-worn channels. Each 

 lake was maintained at a fairly constant level so long as the ice 

 permitted escape of the water only over some lateral pass, and sub- 

 sequently was extinguished with the formation of a lake at a lower 

 level when the ice retreated northward and uncovered a lower 

 outlet. In each of two valleys in the more rugged portion of the 

 mountains to the east, the writer has been able to identify at least 

 a half dozen different levels, and including other portions of the 

 Adirondacks, some twenty glacial lakes have been recognized. 



The South Meadows Lake 

 The highest definite level, as shown by sand plains, terraces and 

 beaches, recognized by the writer in the Adirondacks is one ranging 

 from 1950 to 2210 feet in altitude. When the level was first appreci- 

 ated some hesitation was felt in describing it as a glacial lake bottom, 

 for no shore line features or outlets had been noted. It was con- 

 sidered an outwash plain formed by the glacial streams that flowed 



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