GEOLOGY OF THE LONG. LAKE QUADRANGLE 5OI 



From the present main elevated axis the steeper and shorter stream 

 slopes are those toward the east into the Champlain valley. There 

 is hence a tendency on the part of the east-flowing streams to push 

 their head waters across the divide and establish a new stream divide 

 to the west of the elevation axis. Two great valleys had been pushed 

 through the axis in preglacial times, on belts of weak Grenville rocks 

 and, as stated above, much of the present Raquette drainage above 

 Raquette falls seems then to have gone out to the eastward, and 

 has been turned back to a westerly drainage system by uneven 

 glacial deposits. The Saranac is the only present day stream going 

 to Lake Champlain which crosses the main axis. It is quite certain 

 that in the future others will do the same thing, unless again 

 retarded by further uplift on the east. 



Postglacial topographic changes in the region have been com- 

 paratively slight. A slow uplift of the district has been in progress 

 so that the drainage has had a changing base level throughout the 

 time. The streams, where out of their old courses, or where across 

 old cols, have developed falls and rapids with gorges below, but the 

 rocks are mostly very resistant, even the largest of the streams are 

 of only moderate size, and toward their head waters they are often 

 filtered clear of sediment by passing through lakes. These things 

 all combine to make the amount of postglacial cutting compara- 

 tively slight. Locally the streams have aggraded their valleys, 

 sometimes because of a reversal of direction, at others because of 

 being turned out of their old valleys locally by drift obstruc- 

 tion. Much of the Raquette valley within the quadrangle is of 

 this character. It is a meandering stream on a wide valley 

 floor, bordered by mud banks which fall off to swamps away from 

 the stream, and with frequent cut-off meanders in all stages of 

 filling [pi. 20]. 



A considerable amount of lake filling has also been done, as a 

 moment's inspection of the map will show. The present Tupper 

 Lake reservoir is simply the reexcavated portion of a former pond 

 which had been entirely converted into swamp. It is an interest- 

 ing locality in that there is a well preserved old shore line on the 

 north side marking a former water stage 10 feet above the present. 

 This shore is marked by a boulder accumulation, concentrated 

 there by the washing away of the associated finer material by the 

 action of the waves. 



Even the largest of the lakes are not sufficiently large to permit 



