416 DESCRIPTION OF THE COUNTRY BORDERING 
a few feet above the water-level. The last high mural precipice seen along the 
boundary line was near the lower end of this lake. On the American side is a 
LONG, WOODED SLOPE AND ESCARPMENT OF SLATE. 
ridge of syenite, four hundred feet in height, with a rounded outline and rather 
gentle slopes. 
The thirteenth portage is five hundred and forty paces long, and leads over the 
dividing ridge between the tributaries of Lake Superior and those of Hudson’s Bay 
to Mountain Lake. The rock forming the summit of this ridge is syenite, associated 
with massive hornblende. On the jong point which projects into Mountain Lake, 
near the termination of the portage, the rock (No. 13) is schistose, and alternates 
with thin flinty layers. About a mile below this point, on the north side of the 
lake, is a low exposure of granite (No. 14) which slopes down to the margin of 
the lake. It is in low bosses, from ten to thirty feet in height, which are bare, or 
only covered with mosses and lichens. Back of this is a high ridge, bearing east 
and west, which ascends by a series of steps or plateaus, covered principally with 
mountain ash and small maple. About one-fourth the height of the ridge is a granite 
exposure, in which masses of hornblende rock (No. 16) were found completely 
enveloped. Still higher up, where the hornblende rock (No. 17) is traversed by 
small granitic veins, it becomes somewhat altered in character, and resembles 
diallage rock (No. 15). The top of the ridge is composed of coarsely crystalline 
hornblende (No. 17). This exposure, like the one on the dividing ridge, shows 
clearly the evidence of having been subjected to igneous action since its upheaval. 
I think it highly probable that it had a schistose structure prior to the eruption of 
the granite. On the top, many large, weather-worn fragments of granite occur, 
but no vein of that rock was seen. The outlet of Mountain Lake, which may be 
called the source of Rainy Lake River, is from thirty to fifty yards wide, but at its 
entrance into Flint Lake it is contracted to twenty feet, by a sand point, which 
extends out from the eastern end of that lake. 
On the northwest shore of Flint Lake is an exposure of slaty hornblende (No. 
