112 
COPPER-BEARING ROCKS OF LAKE SUPERIOR. 
Tabulation of the results of a microscopic study of the felsites and felsitic porphyries 
of the Keweenaw Series—Continued. 
| Specimen num- 
ber. 
Place. 
Quarter-section. 
Section. 
Township. 
Range. 
Macroscopic charac- 
ters. 
Microscopic descriptions of thin sec- 
Py 
~ 
(t) 
East side Michipico- 
ten Island. 
Islands off harbor, 
south side of Michi- 
picoten Island. 
Aphanitic; 
Matrix dark pur- 
plish-red, aphani- 
tic; porphyritic 
quartzes extraordi- 
narily abundant, of- 
ten reaching two- 
tenths inchin diam- 
eter. Red porphy- 
ritic feldspars also 
very abundant, two- 
tenths to three- 
tenths inch in 
length. Close to 
1838, 1846d, 1970, 
and 1728. 
light 
flesh-red; very 
rough fracture; re- 
sembles the rock 
from Mount Hough- 
ton, Keweenaw 
Point. 
The groundmass of this rock is faintly 
pinkish-tinted and cloudy; it con- 
tains numerous very minute ferrite 
particles, which, in the vicinity of 
the porphyritic ingredients, show 
crowding and a tendency to linear 
directions. In the polarized light the 
matrix shows a dark background 
strewn with particles and flocks of 
particles of feebly doubly refracting 
substances, but only rarely a dis- 
tinetly recognizable quartz network. 
The porphyritic quartzes are very 
large and abundant, and much eaten. 
The feldspars are also unusually large, 
are both orthoclase and oligoclase, 
and are also much altered. See Fig. 
5, Plate XIII. 
The groundmass is nearly colorless, 
cloudy, and thickly dotted with very 
minute ferrite particles, which are at 
times aggregated into waving lines. 
In the polarized light feebly polarizing 
flecks dot a dark background, some of 
which are recognizable as quartz net- 
work clusters. No porphyritic ingre- 
dients in the section. 
*Macfarlane’s Michipicoten Col. No. 11. ‘‘Felsite porphyry.” Rep. of Progress, Geol. Sur. Canada, 1863-1866, p. 142. 
+ Mactfarlane’s Michipicoten Col. No. 13. 
“Trachytie phonolite.” 
Ibid., p. 142. 
Augite-syenite and Granitell—Occurring abundantly as pebbles and 
boulders in the Keweenawan conglomerates; in great irregular mountain 
masses in the lower part of the series; and again, in plainly intersecting 
masses, and even in thin seams in the coarse gabbros lying near the base 
of the series, on both north and south sides of Lake Superior—are found 
flesh-red to brick-red rocks, which present a plainly, and often quite coarsely 
crystalline structure and general granitic appearance. Red feldspars, un- 
striated alone, or both unstriated and striated together, appear always to 
make up the bulk of these rocks, and quite commonly are the only macro- 
scopically recognizable ingredients. Quartz, however, is often visible, and 
especially in the more coarsely grained and more strongly granite-like 
