464 CHARLES EMERSON PEET 



mon elevation of 220 feet. It stands 20-40 feet above its surround- 

 ings. The top is often quite flat and has been subjected to considera- 

 ble wave-action. The materials are frequently coarse gravel, with 

 occasional large bowlders. A number of wells on this esker are 

 reported by their owners to reach clay after penetrating the gravel. 

 Marine shells are found on the slopes of this esker a few feet beneath 

 the surface. 



The streams and their valleys. — Down the slopes of the higher land 

 the streams extended their courses as the waters of the lake, and sub- 

 sequently the waters of the sea withdrew and exposed more and more 

 of the lake-floor and sea-floor. The courses which the streams took 

 were determined by the slope of the land. Into their deltas the 

 streams have cut valleys, and some have cut, not only through the 

 delta gravels, but also through the underlying till and into the rock 

 below. This is notably true of the Ausable River, which has reached 

 the Potsdam sandstone at a number of places from above Keeseville to 

 Ausable chasm. At the latter place it has cut into the Potsdam rock 

 to a depth of 80-100 feet, causing the falls to recede from their original 

 position at the loyver end of the chasm to their present position one 

 and an eighth miles back. The Saranac River has not only cut 

 through the morainic ridge west of Cadyville, but through the till 

 and into the underlying Potsdam sandstone; again to the eastward 

 it has cut through the upper delta deposits and underlying till into the 

 underlying sandstone. The Saranac from Cadyville downstream 

 some distance, and the Ausable from the lower end of the chasm to 

 some distance above, have remarkably crooked courses, with almost 

 rectangular turns, which have been determined by the joint planes of 

 the rock. (See Fig. 19.) 



Successive stages in the downcutting of their valley-fillings are 

 shown by a series of river terraces on the Ausable above and below 

 Keeseville, on the Salmon River above South Plattsburg, on the Sara- 

 nac above Morrisonville; and doubtless on many other streams. The 

 successive levels of the waters of the lake and of the sea are shown on 

 the streams by lower deltas and by lower bars and beach ridges. 

 Some of these low-level deltas are not simple, but appear to contain 

 glacial deposits buried in and modified by subsequent deposits. 

 This is notably true on the Ausable. 



