116 
COPPER-BEARING ROCKS OF LAKE SUPERIOR. 
irregular masses and thin veins intersecting the coarse orthoclase-gabbro 
of Duluth, Minnesota; the great granite-like mass constituting the bold red 
point three miles above the mouth of Split Rock River, on the Minnesota 
coast; the similar mass on the same coast forming the south point of Beaver 
Bay; the bold point on the shore of section 32, township 56, range 7 west; 
the intersecting masses on the same coast two miles below the mouth of 
Baptism River; and the great mountain mass forming Eagle Mountain, 
Minnesota, thirty miles back from the lake coast. 
Tabulation of the results of a microscopic examination of augite-syenites and granitells 
of the Keweenaw Series. 
Specimen number. 
1903 A 
Place. 
Pebble from con- 
glomerate at 
south foot of 
Mount Bohemia, 
north shore of 
Lac La Belle, 
Keweenaw Point, 
Michigan. 
Quarter-section. 
a 
| Section. 
| Township. 
& 
| Range. 
29 W. 
Macroscopic char- 
acters. 
Microscopic descriptions. 
Angle on| 2. 
cross-hair. s 
Angle between 
maximum ex- 
tinctions of 
adjacent hemi- 
tropic bands of 
the plagioclase 
in sections cut 
at random in 
the zone O; ii. 
osite| c= 
sides of| #2 
Minutely crystal- 
line; pinkish-red, 
mottled with 
minute green 
spots; epidote 
in seams; pink- 
ish feldspars are 
plainly recogniz- 
able as the prin- 
cipal ingredient. 
Appears to be chiefly made up 
of orthoclase and plagioclase 
erystals saturated with sec- 
ondary quartz, which is ar- 
ranged in two ways: Ist. In 
relatively coarse particles 
shaped like the quartzes of 
graphic granite. These par- 
ticles commonly polarize in 
clusters ; they are plainly sep- 
arate from one another in the 
thin section, and therefore 
present quite a contrast with 
the networked quartz so com- 
monly foundin the matrices of 
the felsitic porphyries. 2d. 
In excessively fine radiating 
lines, diverging usually not 
from a point, but from a line, 
producing thus a fan-like ar- 
rangement. This fan-like ap- 
pearance is also brought out 
by the arrangement of the 
minute ferrite particles, by 
which all of the rock, ex- 
cept the large quartzes, is 
stained. That the original 
rock was entirely made up of 
relatively coarse crystals isan 
° ° ° 
25 | 25 | 50 
21) || 21 || 42 
19 | 21 | 40 
1850 |e linse 
19 | 24 | 43 
17 | 16 | 33 
PX an ee) ae 
