ON THE NORTHWEST SHORE OF LAKE SUPERIOR. 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, 36, 
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. . 
a,a. Slate. b. Trap injection. c. Overlying trap. 
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, a. States. 6. Hornblendie 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 
