0 N T il B 



NORTHWEST SHORE OF L A K E S U P E R I 0 R. 



411 



broken ridges, all with mural escarpments looking northwest, as is shown in the 

 preceding sketch. 



The principal rock is argillaceous slate, the upper beds of which are much altered, 

 and overlaid by a tough, coarse-grained greenstone, which disintegrates easily when 

 exposed to the weather, and falls to a dark yellow earth. As a general remark in 

 relation to this rock it may be said, that as the surface of the bed is approached, it 

 always becomes coarser, more crystalline, and weathers more easily. 



The rocks at this place show a very regular gradation from clay slate to horn- 

 blendic slate, and from that rock to common greenstone and syenite. Nos. 35, 30, 

 and 37, show the alterations produced in the lower rocks by the greenstone. No. 

 38 is the lowest slate, and nearly or quite unaltered. No. 39 is within a few feet 

 of the overlying rock, and No. 40 in immediate contact with it. Where Nos. 35 

 and 40 come together, there appears to be a commingling of the rocks, as though 

 the lower rock had been broken up and partially fused by the trap. Where the 

 contact is exposed in the escarpment, the metamorphosed rock assumes the semi- 

 columnar structure of the trap. In the first hill southeast of the lake, the upper 

 slate-beds have been elevated at a high angle by an injection of trap, as shown in 

 the following section. 



Between the range which crosses here, and the one to the southeast, the distance 

 is from ten to twelve miles, and it is in this valley that the swamps mentioned 

 above occur. On the borders of the lake the trap ridges are finely displayed, and 

 the relations of all the rocks shown in the most satisfactory manner in the nume- 

 rous escarpments of both shores, all of which bear a great resemblance to those 

 represented in the sketch taken at the outlet of the lake. 



The sixth portage is five hundred and fifty paces long, and leads to Moose Lake, 

 where the Hudson's Bay Company have a winter house. A great many large frag- 

 ments of slate occur on the portage, but no rock was seen in situ, the density of the 

 forest and undergrowth being so great as to render explorations beyond the portage 

 path almost impracticable. Southwest of the lake a greenstone ridge was seen, 

 which, from its bearing, must cross the portage, and it is accordingly so laid down 



a. Slate. *. Trap injection, c. Overlying trap. 



a 



a. a. Slates, b. Hornblendic rocks. 



on the map. On the borders of the lake the rocks are principally schistose. The 

 lowest rock seen was a very compact, fine-grained, hornblendic slate, overlaid by 

 hornblende rock to the height of one hundred and fifty feet. As the east end of 



