FO needle Tiel 
* 
= Po: Re. 
ILLUSTRATIONS. 
PLATE X—Continued. 
Fig. 3.—Diabase-porphyrite from Duluth, Minn., bed of Brewery Creek. 
S. E. 4, Sec. 22, T, 50, R. 14 W. Porphyritie orthoclase and 
oligoclase, in a base consisting of plagioclase, magnetite, 
augite, and unindividualized substance. Scale, 144 diam. 
Fic. 4.—Ashbed-diabase from Frog Creek, Douglas County, Wis. S. W. 
3, Sec. 28, T. 42, R.11 W. Plagioclase; augite in grains; 
magnetite. Scale, 60 diameters. 
XJ.—Thin section of amygdaloid from the bay above the Great Palisades on the 
Minnesota coast. S. W.4, Sec. 22, T. 56, R.7 W. Unindi- 
vidualized ferritic base with plagioclases; gas cavities filled 
with fragmental material from above, and containing cal- 
cite deposited after the fragmental material. Scale, 24 diam. 
XII.—Thin sections of quartziferous porphyry ........-........------------------ 
Fic. 1.—From Yoreh Lake Railroad, Keweenaw Point. Sec. 36, T. 56, 
R. 33 W. Matrix with particles showing flowage; ortho- 
clase; rounded quartz crystals. Scale, 15 diameters. 
Fie. 2.—From a pebble of the Calumet conglomerate, Calumet Mine, Ke- 
weenaw Point, Mich. Matrix; porphyritic crystals of 
orthoclase and quartz. Scale, 12 diameters. 
Fic. 3.—From the Great Palisades of the north shore of Lake Superior, 
N. E. 3, Sec. 22, T.56, R.7 W., Minn. Matrix showing flow- 
age; porphyritic orthoclase and quartz. Seale, 9 diame- 
ters. 
Fig. 4.—Part of the same section enlarged, showing flowage lines. 
Scale, 32 diameters. 
XIII.—Thin sections of quartziferous porphyry ..........---------..-ses. ---------- 
Figs. 1,2,3,4,and 7 all represent quartzes in the quartziferous porphyry 
of Bead Island, at the mouth of Nipigon Straits on the 
north shore of Lake Superior, Ontario, Canada. Scale, 26 
diameters. 
Fig. 5.—Quartz in quartziferous porphyry from cast shore of Michipicoten 
Island. Seale, 26 diameters. 
Fie. 6.—Quartz in quartziferous porphyry from Baptism River Point, 
north shore of Lake Superior, Minn. S. E. 4, See. 11, T. 56, 
R.7 W. Seale, 26 diameters. 
Fig. 8.—Glass inclusions in the quartz of Fig. 6 greatly enlarged, show- 
ing hair-like devitrification and black hexagonal crystals. 
Seale, 400 diameters. 
Fic. 9.—Banded quartz-porphyry from south side of Great Palisades. 
S. W. 4, See. 22, T. 56, R. 7 W. Drawn from the polished 
surface of a hand specimen. The quartses appear as black 
spots. Natural scale. 
Fic. 10.—Thin section of porphyry shown in Fig. 9, showing flowage 
banding. Scale, 11 diameters. 
Fic. 11.—Portion of the same section further enlarged. Scale, 33 diam. 
Fic. 12.—Portion of the same section enlarged. Scale, 33 diameters. 
Fig. 13.—Purple felsitic porphyry from the bed of Carp River, Porcupine 
Mountains, Mich. N. W.4, Sec. 20, T. 51, R. 42 W. Base 
of unindividualized ferrite-bearing substance charged with 
secoudary quartz; porphyritic orthoclase. Scale, 22 diam. 
Fic. 14.—The same section in polarized light. Scale, 22 diameters. 
Fig. 15.—Pink felsite from north shore of Lake Superior, 8. W. 4, Sec. 
28, T. 56, R. 7 W., Minn. Cloudy base completely saturated 
with unusually coarse networked secondary quartz; ferrite 
particles and strings of particles. Secale, 2 diameters. 
Fig. 16.—Part of the same section further enlarged. Scale, 20 diameters. 
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