106 
Tabulation of the results of a microscopic study of the felsites and felsitic porphyries 
COPPER-BEARING ROCKS OF LAKE SUPERIOR. 
of the Keweenaw Series—Continued. 
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3 
88 Place. ba 
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$ 2 
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1247..| Bed of Little Carp | NE. 
River, Porcupine 
Mountains, Michi- 
gan, 1850 N. 600 W. 
1259..| Porcupine Mountains, | S. line 
Michigan, 270 W. 
1263..| Porcupine Mountains, | SE. 
Michigan, 200 W. 
1621.) Bed of Potato River, | SE. 
Ashland County, 
Wisconsin. 
871I.| Mouth of Tyler’s | SE. 
Fork, Ashland 
County, Wisconsin. 
ee ee eee eee 
& 
a|2 
B/E 
ie) 
a|a 
20 | 50 
9 | 50 
32 | 51 
15 | 46 
17 | 45 
| Range. 
44W 
44W 
43W 
1W 
2Ww 
Macroscopic charac- 
ters. 
Aphanitic; dark pur- 
plish-red; some mi- 
nute porphyritic 
quartzes and feld- 
spars. 
Aphanitic; bright-red 
very plainly banded 
with lighter shades; 
porphyritic white 
orthoclase rather 
abundant, often ly- 
ing across two or 
three bands. 
Aphanitic; dark-red 
closely banded with 
lighter red; no por- 
phyritic ingredi- 
ents. 
Aphanitic; pale lilac- 
tinted base, thickly 
studded with white 
porcellaneous crys- 
tals of feldspar 
reaching one-eighth 
inch in length, and 
smaller black glassy 
quartzes. 
Much altered and soft- 
ened, aphanitic, 
brick-red matrix, 
scattered through 
which are minute 
brighter red ortho- 
clases and very 
abundant larger 
quartzes. 
Microscopie descriptions of thin sec- 
tions. 
Matrix stained.with ferrite, and satura- 
ted with secondary quartz as in the 
last described. There are also some- 
what abundant larger quartz areas, 
apparently also secondary, besides 
which there are the usual sharply 
marked quartzes and feldspars, the 
latter much reddened and altered. 
Here and there a quite perfectly de- 
veloped augite crystal is seen. The 
ferrite particles are arranged so as to 
indicate flowage. 
In the thin section the banding is seen 
to be produced by the presence of 
much oxide of iron in some bands and 
absence of it in others; the latter 
bands are also more highly crystalline, 
but all of the section presents an un- 
usual quantity of individualized mat- 
ter, apparently both quartz and ortho- 
clase. The bands are non-continuous 
even in the breadth of a thin section. 
In the thin section the lighter bands are 
seen to contain much more and rela- 
tively coarser secondary quartz than 
the other bands, which are in turn 
relatively rich in ferrite particles. 
In ordinary light the matrix appears of 
a general gray color, with thickly scat- 
tered ferrite particles, which, for the 
most part transmit a reddish light, 
even when very thick. In polarized 
light this matrix appears to be satura- 
ted with networked quartz. The 
very abundant qnartzes present all 
the usual characters. The feldspars 
are all turbid and appear to be wholly 
orthoclase. Some sections have the 
ferrite particles and the secondary 
quartz arranged in indefinite lines so 
as to suggest flowage. 
The base is like that of the rock last 
described, but is penetrated through 
and through by veinlets of quartz and 
calcite. The ferritic particles are 
more thickly crowded in the vicinity 
of the porphyritic ingredients, and 
now and then show a tendency to a 
lineararrangement. Thequartzesare 
much eaten, and are penetrated to an 
