184 COPPER-BEARING ROCKS OF LAKE SUPERIOR. 
A northern dip of some 60° is also plain. The same beds are exposed on 
the north flank of Mount Bohemia, in the northern part of section 29, in the 
vicinity of the old Mendota mine, which was worked on a north and south 
vein. Immediately about the old mine buildings are exposures of a very 
fine-grained ashbed-diabase. The same beds show on the sides of the 
ravines immediately south of Mount Houghton. 
Still farther south, luster-mottled melaphyrs and olivine-diabases ap- 
pear to predominate. Mount Bohemia—the high point on the north shore 
of Lac La Belle—shows immense exposures of these rocks on its southern 
flanks, where are plainly to be seen all of the characteristics of the mela- 
phyr of the type belt, the Greenstone of the more northern part of Ke- 
weenaw Point. There are also large ledges of the same rock, but crumb- 
ling and much altered, on the bluff rising behind the old smelting works on 
the north side of Lac La Belle. On the north shore of Béte Grise Bay 
again, in sections 25 and 26, where the contact with the Eastern Sandstone 
may be seen, the rocks are prevailingly luster-mottled melaphyrs, though 
much crumbled, altered, and seamed with laumontite and calcite. All of these 
melaphyrs are exceedingly rich in olivine, which, in the thin section, is 
chiefly represented by a brown or red alteration-product. 
Mount Bohemia shows also large exposures of two other rocks, viz: a 
brick-red augite-syenite, or granitic porphyry, and a rather coarsely crys- 
talline, uralitic orthoclase-gabbro. The former of these two is seen on the 
upper part of the mountain, and its relation to the adjoining rocks was not 
satisfactorily made out, though it seems most probable that it is intersecting. 
The other rock shows lower down, on the southeast side of the mountain, 
and appears to constitute an interstratified belt (not impossibly an intersect- 
ing mass). It is the rock on which were chiefly based the statements of 
Jackson, Foster and Whitney,‘ and others, that the Bohemian Range is al- 
together different as to its kinds of rock from the more northern belts. It 
constitutes, however, but a very small portion of the mass of the range, and 
1“The lower portion of the elevation is here made up of a peculiar rock composed of chlorite and 
labrador in nearly equal proportions. These two minerals are each in a distinctly crystalline condition, 
and the feldspathic portion is of a light-reddish color. The mass is filled irregularly with crystals of 
magnetic iron ore, which occasionally form a large portion of the rock. Particles of copper pyrites 
are also scattered through it. This variety of rock seems to pass gradually into the dark-colored, fine- 
grained greenstone which occurs on the summit of the mountain.”—Foster and Whitney, op. cit., p. 65. 
