200 PHYSICAL GEOGRAPHY. 



charging streams taking an opposite direction through the 

 newer deposits. 



Methy Portage forms the dividing brim between the 

 Missinipi basin and the Mackenzie River valley, at the 

 place where it is crossed in the usual canoe route; and, 

 though the country be wooded, it may be considered as 

 a partial extension of the prairie slope. The strata are 

 bituminous shale * resting on silurian limestone, and 

 covered with a thick arenaceous deposit. This is deeply 

 furrowed by the channels of the Elk River, and its tribu- 

 tary the Washacummow ; but the lake basins which mark 

 out the border of the intermediate primitive rocks must 

 be sought for further to the eastward. It is probable that 

 this border touches a straight line drawn from Knee Lake, 

 across the outlet of Athabasca Lake, to the deep northern 

 arm of Great Slave Lake, and onwards by Marten Lake, 

 across the two eastern arms of Great Bear Lake, to the 

 Copper Mountains. That portion of the line which lies 

 between Athabasca Lake and Methy Portage is little 

 known, because the water route lies to the westward of it. 

 Wollaston and Deer Lakes already mentioned, will, if this 

 line be correctly drawn, be situated considerably within 

 the border of the primitive rocks ; and an illustration of 

 the manner in which the waters occupying the minor 

 valleys of that district communicate with each other is 

 afforded by Wollaston Lake sending a stream from its 

 north end into Athabasca Lake, and one from its south 

 end into the different river system of the Missinipi. This 

 fact, which, as reported on the authority of the fur-traders, 

 is expressed in Arrowsmith's map, may be considered as 

 proving that Wollaston Lake is considerably elevated. 



* It is doubtful whether this shale be referable to the Marcellus 

 shale or not. 



