THE ADIRONDACK MOUNTAINS 



65 



the Ice Age. The locations of many such extinct lakes are easily 

 recognized by the more or less well-preserved, typical, flat-topped 

 delta deposits of stratified sands, gravels and clays. Such f^at-topped 

 deposits, always free from boulders and at concordant altitudes in 

 the valleys, mark the former lake levels. The sites of many other 

 extinct lakes are now marked by flat meadow lands or swampy areas, 

 the lakes having been filled by sediments or plant accumulations or 

 by both. Swamps and meadowlands of this sort are exceedingly 

 common throughout the Adirondacks, and constitute one of the 

 characteristic features of the region. 



Perhaps the finest example of a large, wholly extinct glacial lake in 

 the State has been called Black lake which occupied a good portion 

 of the bottom of the Black River valley in the western side of the 

 Adirondacks. The water was held up by a wall of ice during the 

 retreat of the great ice sheet (see figure 11). The former presence 

 of this lake, which covered many square miles, is conclusively 

 proved by the extensive development of delta sand plains on the 

 eastern side of the valley, the delta materials (chiefly sand and 

 gravel) having been brought into the lake by streams loaded with 

 debris from the newly ice-freed Adirondacks. These delta deposits 

 became more or less merged and they now form an extensive sand 

 plain over 30 miles long, several miles wide and fully 200 feet 

 thick on the steep western side (figure 12). 



|°;°»%°.o'| Glacial lake de/f-a deposif 



\\w:.'.\ Osweoo ■sands/'one 



I I Lorraine s/iole if sondsfone 



|-^^ Utica sho/e 



Trenfon //mes-ione 

 Pi:?/ne//a-Louiu///e ///nes^cne 

 ^ Po/eojo/c ^/rofa fconceo/ec/J 



I /l3x| Precambr/'c ro cAs 



Fig. 12 East-west section across the Black River valley, 2>4 miles north 

 of Lyons Falls, showing the terraced character of the Paleozoic strata and 

 their relations to the Adirondack rocks. On the east side, the position of 

 the glacial lake delta deposit is shown. Length of section 12^/1 miles. Vertical 

 scale greatly exaggerated. (By W. J. M.) 



Another fine example of a large extinct lake has been called 

 Glacial Lake Sacandaga. It covered many square miles of the 

 bottom of the broad vallev in which Johnstown, Gloversville and 



