FELSITE AND QUARTZ-PORPHYRY. 105 
Tabulation of the results of a microscopic study of the felsites and felsitic porphyries 
of the Keweenaw Series—Continued. 
' z 8 
: : 3 S Macroscopic charac- | Microscopic descriptions of thin sec- 
28 Place. aes ee ters. , tions. 
| ; a |SlEl é 
7 é & |2\a| 2 
} . tions. The porphyritic quartzes are 
very large and commonly much eaten, 
with the usual embayments and in- 
clusions of the matrix. The feldspara 
are chiefly oligoclase, rarely ortho- 
clase; both always much clonded 
: from alteration. There are also pres- 
ent rare porphyritic augites, largely 
replaced by a black opaque substance. 
See Fig. I, Plate XII. 
1970..| Pebble from the Calu- 23 | 56 |33W.| Matrix dark reddish- | Differs from the preceeding only in hav- 
met conglomerate, brown, aphanitic; | ing much less of the whitish individu- 
Keweenaw Point. sharply angular con- alized areas in the matrix, nearly the 
choidal fracture; | whole of which presents a brownish 
very abundant pink staining and produces no definite effect 
feldspars up to one- on polarized light. The ferrite needles 
half inch in length, are also somewhat more minute than 
also black quartzes in the preceeding section. One of the 
> one-tenth to two-| quartzes carries a sharply ontlined, 
| tenths inch in di- fresh, brilliantly polarizing augite 
: ameter; resembles crystal, the augite crystals of the ma- 
1846 d. 
2514..| Porcupine Mountains, | N. line. | 5 | 50 |43 W.| Aphanitic; pale-lilac; 
Michigan, 2000 N. no porphyritic in- 
700 W. gredients. 
2551..| Bed of Carp River,| NW. | 35 | 43 |43W.| Aphanitic; dark pur- 
Poreupine Moun- plish-red; no por- 
trix being wholly replaced by a black- 
ish substance. See Fig. 2, Plate XII. 
Nearly colorless, faintly tinted with 
pink; minute tabular feldspars; some 
networked secondary quartz; some 
non-polarizing material; opaque fer- 
rite particles not abundant. 
Blotched red and colorless ; the reddish 
tinted portions chiefly non-polarizing, 
tains, Michigan, 1420 phyritic ingredi- the white portions composed entirely 
N. 1400 W. ents. of individualized, often relatively 
coarse quartz and orthoclase; net- 
worked secondary quartz rare; fer- 
rite particles not abundant. 
2574..| Porcupine Mountains, SW.| 20 | 51 | 42W]| Aphanitic; dark pur- | Thickly studded with minute brown 
Michigan, 500 N. plish-red; afew mi- ferrite particles, which are also aggre- 
rn 1450 W. nute dark quartzes. gated into large patches; appear- 
ance in ordinary light pretty homoge- 
neous. In the polarized light the ma- 
trix is seen to be completely saturated 
with secondary quartz, which pre- 
sents iteelf in irregularly rounded 
areas each of which is a closely in- 
volved network of non-polarizing 
base and quartz. All of the quartzin 
one of these areas polarizing together, 
. it follows that it all belongs to one 
- individual. A few minute, altered 
porphyritic feldspars. 
ee 
