Temagami-TemisTcaming District^ Ontario. 27 



the lake ; from here it gradually sliallows and opposite the 

 mouth of Montreal River is 350 feet deep. At the point B 

 on the map, old Fort Narrows, there is a very marked contrac- 

 tion, owing to a heavy deposit of sand and gravel in the trench 

 at this place. The depth on this is perhaps 50 feet and the 

 lake again deepens to the north but does not reach the great 

 depths of the lower part. It is also to be noted that where 

 these great depths were obtained it was not only in the middle 

 of the channel but close up to either shore. 



From what has been stated it will be seen that the total 

 depth of the trench, or rather canyon occupied by the lake, 

 fi'om the surface of the old upland to the lake bottom, is about 

 1000 feet at the deepest point, shallowing gradually either 

 way, north and south. At the deepest point the former can- 

 yon is about one- half tilled with water. 



What is the origin of this lake ? For one of its size and 

 nature in this region three possibilities present themselves : it 

 may be a rock basin cut by the ice sheet ; it may be a river 

 valley dammed by glacial drift, or it may be a warped valley. 

 In regard to the first, since tlie general direction of flow of 

 the ice sheet w^as toward the southwest or more accurately 

 S. 14° W., as given by Barlow, it is inconceivable that it 

 could have cut such a deep and narrow gorge transverse to its 

 direction of flow. Barlow's list of glacial striae shows, as 

 might be expected, that in the upper, wider portion of the lake 

 valley the topography exercised enough control to produce an 

 undercurrent in the ice, trending to the southeast. As the 

 valley contracts this becomes less evident and the western bank, 

 with striae in the direction of southwest flow, shows it was 

 receiving the impact of the general moving ice sheet. In 

 such a narrow, constricted gorge the local sub-current might 

 be ex]3ected to die out, the trench would become packed with 

 nearly motionless ice, up to the average level of the plateau,, 

 which would support the ice-sheet moving transversely across it. 

 It seems improbable, therefore, not only that the basin was cut 

 by the ice, but even that the pre-glacial valley was to any great 

 extent deepened by its scour. The general appearance of the 

 gorge, and the lack of truncated spurs, seems also to indicate no 

 great amount of glacial control of its topography. It probably 

 existed pretty much as it is to-day before the advent of the 

 continental ice-sheet. 



The explanation of a morainal dam also seems improbable 

 when one considers the depth of the lake, the fact that the 

 deepest part is not near the outlet but near the middle, and the 

 character of the river bed below the outlet. There is no direct 

 evidence of such a dam, and, as Barlow* remarks of the river 



*Loc. cit. p. 171. 



