104 
COPPER-BEARING ROCKS OF LAKE SUPERIOR. 
Tabulation of the results of a microscopic study of the felsites and felsitic honphyrice of 
the Keweenaw Series. 
| Specimen num- 
ber. 
1909... 
1908... 
1846 
1838.. 
Place. 
Mount Houghton, Ke- 
weenaw Point, 
Mount Houghton, Ke- 
weenaw Point. 
Pebble from Eagle 
River conglomerate; 
mouth of Eagle 
River, Keweenaw 
Point. 
Torch Lake Railroad, 
Keweenaw Point. 
| Quarter-section. 
W. line. 
W. line. 
NW. 
S. part. 
Section. 
Township. 
Range. 
Macroscopic charac- 
ters. 
nt 
= 
24 
19 
36 
58 
29 WwW. 
20 WwW. 
31W. 
33 W. 
Aphanitic; pink to 
brick-red; no visible 
porphyritie ingredi- 
ents; very hard. 
SiO2, 76.9 per cent. 
Difficultly fusible. 
Aphanitic; hard, 
light-pinkish; sharp- 
ly angular fracture ; 
no porphyritic ingre- 
dients. SiO,, 77.2 
per cent. 
Matrix aphanitic, pur- 
plish-red, hard; 
abundant large 
black quartzes and 
flesh-red feldspars. 
Aphanitic; dark-red, 
hard; very abun- 
dant and large, 
black, porphyritic 
quartzes reaching 
two-tenths inch in 
diameter, and red 
feldspars two-tenths 
to one-quarter inch 
inlength. Some of 
the feldspars are 
plainly striated. Re- 
sembles 1970 and 
1846 d. 
Microscopic descriptions of thin sec- 
Much non-polarizing matter, through 
which are seen scattered, when 
viewed between the crossed nicols, 
minute bright points and lines; also 
a few relatively large, scattered nests 
of aggregated particles of quartz. The 
whole section is stained with red 
ferrite, which is also aggregated in 
numerous irregular, opaque particles. 
This section differs from the preceeding 
in containing much less red ferrite, 
and less non-polarizing matter; and 
in containing many polarizing parti- 
cles often arranged in a felt-like mass. 
Many of the particles are plainly 
tabular feldspars. 
The matrix is much stained with red 
ferrite, and shows but feeble polariza- 
tion in flocks of small particles ; some 
small non-polarizing areas. In addi- 
tion to the general red stain are abund- 
ant brown and black, opaque ferrite 
particles. Porphyritic quartzes large, 
in the usual doubly terminated crys- 
tals, with embayments and inclusions 
of the matrix. The porphyritio feld- 
spars are oligoclase. Augite occurs 
also porphyritically in particles as 
large as the quartz, and with rounded 
contours; these augites are filled 
with a brown, ferritic .alteration-pro- 
duet. 
Matrix irregularly mottled pink and 
nearly colorless, these mottlings being 
so arranged as to suggest flowage. 
The darker portions of the matrix 
are thickly studded with minute fer- 
rite needles, so arranged as to empha- 
size the fluidal structure very strong- 
ly, especially in the neighborhood of 
the porphyritic quartzes. The darker 
portions of the matrix affect the polar- 
ized light only in a few minute points. 
The lighter portions, on the contrary, 
appear to consist of wholly individu- 
alized quartz and orthoclase confused- 
ly intererystallized. Calcite is also 
occasionally seen in these lighter por- 
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