82 
COPPER-BEARING ROCKS OF LAKE SUPERIOR. 
Tabulation of the results of a microscopic study of diabase-porphyrite and ashbed-diabase 
—Continued. 
5 
E Place. g es char- 
lige 2 | |s 
z |e /s]e] 3 
n CC |n)|aA!] & 
| ee 
2560.... Porcupine Mount- | NW. 23 | 51 43 W.| Aphanitic; dark 
ains, Michigan. | purplish-brown; 
conchoidal frac- 
ture; carries 
minute porphy- 
ritic feldspars. 
SiOz, 59.38 per 
cent. 
1245...| Falls, Little Carp | SE. | 17 | 50 |44.w.| Nearly aphanitic; 
River, Poreu- | dark-brown; 
pine Mount- conchoidal frae- 
ains, Michigan. ture; numerous 
porphyritic feld- 
spars. 
2568... Porcupine Mount- | NE. | 23 | 51 |43W.| Aphanitic; dark 
ains, Michigan. | chocolate- 
| brown; holds 
minute porphy- 
ritic feldspars. 
2062 's.|.c sen G0esceseeeens NW.) 24 | 51 43 W.) Aphanitic; dark- 
brownish to 
black. 
Composition as determined by 
the microscope. 
Angle between 
maximum ex- 
tinctions of 
adjacent hemi- 
tropic bands of 
the plagioclase 
in sections cut 
at random in 
the zone O: ii. 
Groundmuss:—plagioclase, in 
very minute tabular crystals; 
unindividualized substance ; 
magnetite; much red and 
brown ferrite; rare and bril- 
liantly polarizing particles be- 
longing to augite; secondary 
quartz. Porphyritic ingredi- 
ents:—rather rare orthoclases 
and oligoclases; much rarer 
augites ; pseud-amygdules of 
calcite. i 
Groundmass :—in ordinary light, 
much stained with ferrite; 
consists of unindividualized 
substance, oligoclase, magnet- 
ite, and ferrite recognizable; 
augite particles very rare. 
Porphyritic ingredients :—or- 
thoclase and oligoclase very 
abundant; augites rarer, of 
good size, almost wholly al- 
tered to ferrite and green sub- 
stance. 
Groundmass as in 2560. Porphy- 
ritic feldspars larger and more 
abundant; the augite com- 
monly much altered to green- 
ish substance with bands of 
red and brown ferrite. 
Groundmass :—plagioclase ; un- 
individualized substance; mag- 
netite ; ferrite ; augite, in mi- 
nute, not abundant grains, 
often altered to a green sub- 
stance; secondary quartz. 
Porphyritic ingredients:—not 
very abundant, good-sized or- 
Angles on| < ; 
opposite om 
sides of rs 
cross-hair.| © 
° ° ° 
8 9 17 
2 5 7 
5 6 ll 
thoclases and oligoclases, much |_ 
altered to chlorite; augite, 
much altered to green sub- 
stance with bands of ferrite. 
