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FELSITE AND QUARTZ-PORPHYRY. 107 
Tabulation of the results of a microscopic study of the felsites and felsitic porphyries 
Place. 
ber. 
imen num- 
Spec 
8008.) Clam Falls District, 
Polk County, 
Wisconsin. 
708...) North shore Lake Su- 
perior, two miles 
above mouth of Split 
Rock River, Minne- 
sota. 
711...) North shore Lake Su- 
perior, one-quarter 
mile east of 708. 
730...) Bed of Split Rock 
River, Minnesota. 
790...| South shore of Beaver 
Bay, Minnesota. 
Quarter-section. 
Nw. 
NW. 
Nw. 
SE. 
of the Keweenaw Series—Continued. 
Macroscopic charac- | Microscopic descriptions of thin see- 
ters. 
12 | 37 | 16W| Aphanitic; pinkish- 
13 | 54) 9 W. 
13 | 54) 9 W. 
1| 54/9 W. 
12 | 55|8 W. 
red matrix with mi- 
nute feldspar faces. 
Aphanitic ; brick-red, 
much decomposed 
and softened. Car- 
ries minute pink or- 
thoclases. 
Light-red; obscurely 
banded with dark- 
red ; aphanitio; sub- 
conchoidal fracture; 
carries abundant 
irregular, black, 
hair-like markings. 
Aphanitic; dark red; 
conchoidal frac- 
ture; carries min- 
ute red feldspars. 
Aphanitico; light- 
gray, banded with 
non-continuous 
pinkish bands, the 
middle portion of 
each band being oc- 
cupied by a quartz 
seam. 
tions. 
extraordinary extent by club-shaped 
masses of the base. The orthoclases 
are very much reddened and kaolinized. 
Several inclusions of partially devitri- 
fied glass were found in the quartzes. 
A few porphyritic augites, largely al- 
tered to red iron oxide are contained. 
The thin section shows a matrix com- 
pletely saturated with a network of 
secondary quartz; the quartz network 
is coarser than usual. Theporphyritio 
feldspars are wholly triclinic. 
Matrix largely of non-polarizing ma- 
terial stained red, and containing min- 
ute tabular crystals, also areas of sec- 
ondary quartz. Confusedly inter- 
mingled with these deeper colored 
areas are lighter ones, occasionally 
colorless, in which there is a larger 
proportion of individualized material, 
apparently quartz. The section is 
dotted throughout with minute points 
of ferrite. The porphyritic ingredi- 
ents are orthoclase and oligoclase in 
not very abundant, small, and much 
altered crystals, some of which pre- 
sent the appearance of having been 
much fractured before the solidifica- 
tion of the matrix. 
Similar to 708, but with very much 
more secondary quartz. 
Near to708 and 711, with the red staining 
more general ; in other words, there is 
but little of the lighter tinted, more 
individualized material; secondary 
quartz throughout in minute arbores- 
cent clusters. 
Colorless, merely varying in transpar- 
ency. Themore transparent portions, 
which are distinctly arrangedin bands, 
are composed of quartz in relatively 
large areas. The clouded bands pre- 
sent, in the polarized light, a dark 
background, thickly crowded with 
minute polarizing points which are in 
