300 G. 8. Hume — Stratigraphy and Geological Relations 



river has been much overdeepened. This is the more 

 striking when it is considered that this portion of Lake 

 Timiskaming represents a trench with rugged shores that 

 rise 400-600 feet to the elevation of the Laurentian 

 plateau. 



Various theories such as warping (Pirsson 1910) and 

 glacial scour have been advocated to explain this over- 

 deepening, but no very satisfactory conclusions have been 

 obtained. As the continental glaciers moved in a direc- 

 tion S. 7° W. to S. 18° W. (Barlow 1897), or across the 

 Timiskaming trench, the theory of ice action has been 

 rejected for the most part. However, lists of striae made 

 by Barlow clearly show that a subcurrent of ice was de- 

 flected down the Timiskaming trench, and it is suggested 

 here that glacial scour on the fractured and broken mate- 

 rials south of the intersection of the three regional frac- 

 ture systems at the mouth of the Montreal river has been 

 responsible for the overdeepening that is now evident 

 from numerous soundings. At the north end of Lake 

 Timiskaming, the western shore is now known to be the 

 result of a fault of 800-1000 feet displacement. It is 

 therefore of some significance that the deepest soundings 

 south of the Montreal river are invariably found towards 

 the western side of the lake. However, as yet, faulting in 

 this part of the Timiskaming trench has not been actually 

 demonstrated. 



Character of the Paleozoic Floor. 



When the transgression of the middle Ordovician sea 

 overspread the continent from the Arctic, it advanced 

 over a land mass that had much the same sort of relief as 

 is found on the present Laurentian plateau. The surface 

 was very irregular and in the Timiskaming area knobs 

 and ridges that were more than 200 feet high may have 

 been islands during the early submergence. There is a 

 fringe of Ordovician rocks on the north shore of Bryson 

 island, where these rocks everywhere dip away from the 

 island 10° to 12°. Precambrian rock, which forms the 

 main portion of the island, rises 190 feet above the water 

 level, the slope of the Precambrian surface on which de- 

 position took place being responsible for the dip of the 

 Ordovician strata. As Bryson island has been rounded 

 off: by glacial action, it is probable that the relief of the 



