210 COPPER-BEARING ROCKS OF LAKE SUPERIOR. 
sionally visible a very distinct, but more or less irregularly curving, fine 
banding, such as is often found in similar porphyries from other regions, 
and which must be attributed to flowage in a molten state. Occasionally 
the matrix shows a tendency to a more distinctly crystalline texture, the 
rock tending towards granitic porphyry. 
I have examined a number of thin sections of the Porcupine porphy- 
ries, with the following results. The first is pale-lilac felsite (2,514) from 
the large vertical walls on the north slope of the hill on the north line of 
Sec. 5, T. 50, R. 43 W., at 700 paces west of the northeast corner. It 
shows a colorless base without porphyritic ingredients ; and is apparently a 
minutely crystalline admixture of quartz and feldspar. Some of the quartz 
is secondary. Sparsely scattered through the matrix are black and brown 
opaque particles. The bright-red, blotched, rough-textured felsite (2515) 
from the same hill in the S. E. 4, Sec. 35, T. 51, R. 43 W., (250 N., 900? 
W.), shows in the section very much the same appearance as the last de- 
scribed, but contains also some non-polarizing base. The lilac felsite (2516) 
brought from the continuation of the same great ledge in the 8. W. 4, Sec. 
35, (500 N., 1100 W.) gives the same section as the last. The rock 
(2517) from the hundred-foot cliff, near the middle of the same section (720 
N., 1000 W.) is somewhat different. Macroscopically it is an aphanitic 
bright-red rock blotched with white, and without porphyritic ingredients. 
In the thin section the red portions are excessively fine-grained and even 
non-polarizing, with abundant, minute, brownish, opaque particles and parti- 
cles of red oxide of iron. The white portions consist of comparatively large 
particles of orthoclase ‘and quartz. The dark purplish-red rock (2551) 
from the bed of Carp River, in the N. E. 4, Sec. 35 (1420 N., 1400 W.), is very 
much the same felsite as those first described, being without porphyritic 
ingredients. The rock on the south side of the Carp Lake road in the S. E. 
4, Sec. 24, T. 51, R. 43 W., (800 N., 800 W.), is dark purplish-red with a 
few small red feldspars and minute quartzes. In the thin section the matrix 
presents an interesting appearance. Much of it is of a faint reddish tint 
1These numbers refer to specimens, many of which will be found described in the tables of Chap. 
III. 
2These numbers give the distances north and west from the southeast corner of the section, in 
each case. 
