34 NEW YORK STATE MUSE*JM 



moraines; some occur in hollows in the surface produced by the 

 uneven deposition of sand deltas by the overloaded streams of the 

 period of withdrawal of the ice; others are due to the damming 

 T)ack of a valley's drainage by such sands across the valley; yet 

 •others may be due to other causes. 



There is yet no evidence that any of them occupy rock basins, 

 though it is by no means impossible that such may be the case. 

 Big Tupper and Lower Saranac lakes may prove to belong to 

 this category. 



Streams. During the withdrawal of the Laurentide glacier from 

 the northern Adirondacks, the preglacial stream courses cut in 

 the valley base level were completely filled by the glacial deposits, 

 while at the same time the irregular floor of the valley base itself 

 was covered and evened by them. After the departure of the ice 

 the courses of the streams were determined by the slope of these 

 deposits, this slope being in large measure independent of the 

 former channels, so that between the present and former courses 

 there is considerable discrepancy. The slopes of the glacial de- 

 posits in the valleys were gentle, lakes occupied the hollows much 

 more numerously than at present, and the new streams obtained 

 steep grades only after they emerged from the hills on the slopes 

 leading down to the Champlain or St Lawrence valleys. Their 

 profile was convex, rather than concave, and so it remains to a 

 large extent today, while in mature stream valleys the profile is 

 -concave. 



The main streams of the region are of quite respectable size, 

 and their fall is great. The Saranac river from Lower Saranac 

 lake to Lake Champlain, in a course of about 75 miles by the river, 

 lias a fall of 1450 feet, or 20 feet to the mile. The Ausable from 

 Lake Placid down, has a greater fall than the Saranac by 300 feet 

 in a course from 5 to 10 miles shorter. The Racquette and St Regis 

 rivers have a slope slightly less steep than that of the Saranac, 

 but only slightly. These are very considerable slopes for streams 

 of such size, and excavation of their beds is going on at a quite 

 rapid rate. At first their courses were wholly in the unconsoli- 

 dated drift deposits. These were quickly cut into, and soon the 



