.".mi K. BELL — GLACIAL PHENOMENA IN CANADA. 



tioned the dips and flexures of the strata, lines ol crushing or fissures, with 

 or without igneous injections, and unequal hardness of the rock — <>r rather 

 its unequal susceptibility to decay. I have often noticed that lines of 

 crushing which might nol otherwise have been very observable are of much 

 importance in promoting the decay of the rock, preparatory to it- removal 

 by glacial denudation, the differenl Btages of the process being observable 

 iu the northern regions. The influence of dikes of breccia, trap, syenite, 



etc., in inection with erosion has been very considerable in determining 



the topography. The large and small dikes have frequently produced oppo- 

 site effects. The former, being coarsely crystalline and decaying easily, have 

 given rise to long valleys, now occupied by rivers or lakes, while the smaller 

 one-, being close-grained, tough, and generally resisting disintegration well, 

 have protected other rocks from the force of the glaciers, and they are now 

 marked by ridges or by the chutes and falls which they cause in the rivers 

 crossing their courses. 



The effeel of large dikes in thus producing channels for water is very 

 conspicuous in some sections of the Mattagami river, as described in my 

 Geological Survey report for 1875. In my report for l' s 7<> I pointed out 

 that the trough of Long lake, more than fifty miles in length and running 

 a! right angles to the strike of the crystalline rocks of the region, lies along 

 the course of an Immense dike, [n 1878 the long, straighl channel of Nelson 

 river, from Bipi-wesk to Split lake, was shown to he due to a similar cau.-e. 

 Anion- other long sheets of water which have been excavated upon the run 

 of large dikes may he mentioned < >ha lake, north of Michipicoten ; Poga- 

 masing lake, mar the intersection of the main line of the Canadian Pacific 

 railway ami the Spanish river; Onaping lake, a narrow channel thirty miles 

 long, lying north of a station of the same name on the railway just men- 

 tioned; ami Matatchewan lake, at the great bend of Montreal river. And 



I have no doubl that almost all tin' lakes of this Arehean region which are 

 tolerably straighl and \-i\y long in proportion to their breadth will !>■■ Pound 

 to occupy channel- originally due to the existence of large dikes. Among 

 -mli lakefi may \»- named the Long lake, west of Lake of the \Y I-. and 



Lake Temiscaming on the Ottawa. The gorge of the Sagnenay, and even 

 that of Hudson's strait, may be due to similar causes. The narrow rocky 

 arm ol ' ian hay which receives the Maganatwan river is situated upon a 



rift iu the gneiss, filled in places with breccia, resulting perhaps from the grind- 

 in"- of its wall-. It is probable that similar inlets in the vicinity, such as Col- 

 line inlet, The Key, ami the peculiarly straight intersecting channel- of the 

 mouth of tin- French river, originated in Bimilar fissures. M r. E. B. Borron, J. 

 P., w ho has travelled much in the regions north of lakes Huron and Superior, 

 inform- us that he ha- 31 . n 30 many instances confirming the above \ iew as 

 to the origin of straighl river-courses and long narrow lakes that he regards 

 ii j- mi . stablished lad in regard to the topography of the country. 



