320 COPPER-BEARING ROCKS OF LAKE SUPERIOR. 
than that of the shore, being at times even due east. Since the coast line 
itself is trending here only some 20° to 25° north of east, it follows that each 
bed makes a yery long exposure on the coast. Felsite and quartziferous 
porphyry have a great development between Grand Marais and the Brulé 
River, the ledges on the coast being usually comparatively low and often 
partly concealed by shingle beaches. On the Devil’s Track River, how- 
ever, the exposures are on a grand scale. 
Quartziferous and granitic porphyries show again in the vicinity of the 
large bay in the east part of T. 62, R. 4 E., and again at Red Rock Bay in 
the Indian reservation (S. E. 4, T. 63, R. 5 E.). The remainder of the 
coast between here and Grand Marais is formed chiefly of coarse black 
gabbro. 
In the angle of the coast immediately below Grand Marais, 8S. W. 4, 
Sec. 21, T. 61, R. 1 E., red felsite is cut by dikes of dark-colored rock, and 
the same thing recurs for two or three miles down the coast, the dikes pro- 
ducing projecting points and the felsite weathering down into shingle beaches. 
The shore-cliff just beyond Grand Marais is red felsite for a length of sev- 
eral hundred paces in a northeasterly direction. At the southwest end of 
the cliff is a broad dike composed of a medium-grained olivine-diabase, of 
which the surface presents a mottling like that of the luster-mottled mela- 
phyrs. The olivine is wholly altered to a brownish substance, but the other 
ingredients are quite fresh. Near its junction with the red felsite this rock 
becomes finer in grain, until at the contact it merges into an aphanitic dia- 
base-porphyrite, with much greenish alteration chlorite. 
At the northeast end of this cliff is another broad dike of similar char- 
acter, with two or three narrow ones, from a mere seam to one or two feet 
in width. The rock of these narrow dikes is a dense diabase-porphyrite 
with much non-polarizing matter in the base. The felsite cut by these dikes 
presents a quite distinct, though irregular, dip towards the lake, and has 
the usual wave-like pseudo-lamination markings. It presents the appear- 
ance of a hardened mud rock more here than at most points where the 
felsites were observed. In the thin section is shown a base with much non- 
polarizing material, with the usual ferritic devitrification-product, and much 
