﻿GEOLOGY OF THOUSAND ISLANDS REGION 1 27 



west. The presence of this divide, with its sharply cut ravines 

 heading against it on both sides is to us one of the most interest- 

 ing features of our district. It is most unfortunate that the maps 

 of the quadrangles next east are not available so that it could 

 be further traced in that direction. Inspection of the Alexandria 

 and Theresa maps will show plainly its course across them. In 

 the low grounds near the St Lawrence the ravine heads are not 

 prominent, though the two lateral ravines into Cranberry creek 

 valley from the east are good examples. But at Browns Corners, 

 4 miles southeast of Alexandria Bay, is seen the head of the first 

 of a series of sharply cut valley heads with northeast trend. The 

 next is at Plessis, dropping down sharply into the Clear lake-Mud 

 lake-Butterfield lake valley, with a secondary sharp drop at the 

 head of Butterfield lake. One and one half miles southeast of 

 Plessis, on the extreme south margin of the Alexandria sheet, 

 is the head of the Hyde lake- Hyde creek- Perch river valley, on 

 the other side of the divide, belonging to the "southwest drainage. 

 Just east are two sharply cut ravines heading on opposite sides 

 cf a low pass across the divide, the valley of Crystal lake, which 

 is tributary to the Mud lake valley, and the valley without pres- 

 ent drainage, followed by the railroad and leading south into the 

 Indian river valley on the Theresa sheet. This valley is some- 

 what more blocked by drift than the others and seems to have 

 held a shallow lake. The Millsite lake and Sixberry lake valleys 

 also head sharply against the divide on the north. They are 

 however of somewhat abnormal type. Most of the other valleys 

 mentioned commence as distinct but shallow, rock-cut trenches, 

 which, after a short course, suddenly deepen to gorges with walls 

 from 40 to 100 feet high. The Clear lake and Hyde lake valleys 

 nicely illustrate this type. The lakes are at the heads of long 

 valleys leading away from the divide. The Crystal lake, Six- 

 berry lake and Millsite lake valleys, on the other hand are short 

 valleys, tributary to others at the side, and they deepen almost 

 at once, instead of having the preliminary shallow course. The 

 view of the head of Crystal lake valley [pi. 34] gives an excellent 

 idea of the general character. 



Passing to the Theresa sheet, attention is at once directed to 

 the considerable and deep valley, leading north past Theresa, the 

 valley into which the modern Indian river breaks at that point, 

 with production of falls and short gorge [pi. 32]. The valley it- 

 self heads 3 miles further south. Two miles to the west is the 

 Hyde creek-Perch river valley, running southwest and heading 



