Xxil ILLUSTRATIONS. 
Pratt VI.—Thin section of very coarse orthoclase-gabbro, from near Duluth, Minn. 
N. W. i, Sec. 28, T. 50, R. 14 W. (1800 N. 2000 W.). Oligo- 
clase; some orthoclase ; diallage, largely altered to uralite, 
which on cross-section shows the hornblende cleavage; 
titaniferous magnetite mostly surrounded by a border of 
brown oxide of iron, iu which are developed biotite blades; 
very large apatites; a little chlorite; rare pyrite particles 
surrounded by an ocherous alteration. Scale, 10 diameters. 
VII.—Thin sections of hornblende-gabbro and of anorthite rock... .-.. paccomesacao 
Fic, 1.—From Ashland County, Wis. N. W. cor. Sec. 35, T. 45, R. 4 W. 
Labradorite; orthoclase; augite partly altered to viridite 
and uralite; brown hornblende in and away from the 
augite; titaniferous magnetite; apatite. Scale, 36 diame- 
ters. 
Fic. 2—From Ashland County, Wis. N. line of N. W. 4, Sec. 17, T. 44, 
R.8W. Oligoclase; orthoclase; brown hornblende; dial- 
lage altered to green uralite; titaniferous magnetite; rare 
quartz; very abundant and large apatites. Scale, 26 diame- 
ters. 
Fic. 3.—From English Lake, at outlet, S. 4, See. 5, T. 44, R. 3 W., Wis. 
Brown hornblende grading iuto augite; labradorite; mag- 
netite. Scale, 23 diameters. 
Fic 4.—Anorthite-rock from north shore of Luke Superior. N. 4, 8. W. 
3, Sec. 5, T. 54, R.8 W. Seale, 17 diameters. 
YVIII.—Thin sections of pseudamyydaloidal diabase and diabase -.-.---..--.----.--- 
Fig. 1.—From Union Mine “vein,” N. W. 4, Sec. 27, I. 51, R. 42 W. (1950 
-N. 1750 W.), Poreupine Mountains, Mich. Oligoclase or 
labradorite; augite wholly altered to green and brown 
pseudomorphs; calcite; chlorite pseudamysdules. Scale, 
26 diameters, 
Fic. 2.—From the Fond du Lae Mine, Douglas County, Wis. N. E. 4, 
Sec. 8, T. 47, R. 14 W. Oligoclase; augite altered to red- 
dish brown pseudomorph; magnetite; pseudamygdules of 
chlorite and epidote. Scale, 28 diameters. 
Fic. 3.—From near the Gogogashugun River, Wis. Sec. 16, T. 46, R. 2 
E. Oligoclase, largely altered to chlorite; magnetite in 
rod-like forms; augite; chlorite pseudamygdules. Scale, 
36 diameters. 
Fig. 4.—Diabase from north shore of Lake Superior below mouth of 
Split Rock River. . S..W. }, See.5, T. 54, R. 8 W. - Labrador- 
ite, in small tabular crystals arranged in a common direc- 
tion; augite, including many labradorites within each crys- 
tal; magnetite, very abundant in the interspaces of the 
augites. Seale, 42 diameters. 
IX.—Thin section of fine-grained olivine-diabase or melaphyr from the north shore 
of Lake Superior, Minn. S. E. }, Sec. 9, T. 51, R. 12 W. 
Augite in large areas, including many plagioclases; anor- 
thite; olivine and magnetite, chiefly in the interspaces of 
the augites; chlorite pseudamygdules. Scale, 20 diameters. 
X.—Thin sections of diabase-porphyrite and ashbed-diabase ...--.....------------ 
Fic. 1.—Diabase-porphyrite from the southeast shore of Michipicoten 
Island. Base of red and brown stained unindividualized 
material, minute plagioclases and black magnetite. Por- 
phyritic labradorite and altered augite. Scale,7 diameters. 
Fic. 2.—Part of the same section enlarged and as seen between the 
crossed nicols. Seale, 21 diameters. 
Page. 
an 
a 
G1 
38 
