CBE UsSsT RATION S. 
PLaTE I.—General geological map of the Lake Superior Basin. Scale, spahony 
II.—Thin sections of olivine-free' gabbros - 2... ..---. 2 cec0 cenccs concee cn ccce once 
Fie. 1.—From half a mile southwest of south point of Beaver Bay, Minn. 
N. W. 4, Sec. 3, T. 55, R.8 W. Anorthite; non-diallagic 
augite. Scale, 21 diameters. 
Fig. 2.—The same in polarized light. Scale, 21 diameters. 
Fic. 3.—From the North Shore, near Duluth, Minn. N. W.4, Sec. 24, T. 50, 
R. 14 W. Anorthite; diallagic augite; titaniferous mag- 
netite; altered olivine. Scale, 30 diameters. 
Fic. 4.—The same in polarized light. Scale, 30 diameters. 
Tit:—Thini sections) of; olivine-pabbrosm.cns2s----sc-cesee «oo seecsoetieecsasscecee 
Fig. 1.—From bed of French River, Minn. N. line, N. E.4, Sec. 7. T. 51, R. 
12W. Anorthite; diallage; olivine. Scale, 25 diameters. 
Fic. 2.—The same in polarized light. Scale, 25 diameters. 
Fie. 3.—From the north shore of Lake Superior, near the east point of 
Sucker River Bay, Minn. S. E. 3, Sec. 2, T. 51, R. 12 W. 
Anorthite ; diallage ; titaniferous magnetite ; olivine. Scale, 
25 diameters. 
Fic. 4.—Large olivines from the same rock as represented in Figs. 1 and 2. 
Seale, 21 diameters. 
IV.—Thin section of coarse olivine-gabbro from Bladder Lake, Ashland County, 
Wis. Labradorite; augite; diallage; olivine, mostly fresh, 
but partly altered to biotite, viridite, tale and iron oxide; 
titaniferous magnetite. Scale, 10 diameters ...-......-..- 
V.— Dhin'sections of. orthoclase-gabbro!- «22-2. 222s ence one concen eee eens cses 
Fig. 1,.—From near Lester River, Minn. N. E. 4, Sec. 29, T. 51, R. 13 W. 
Labradorite; orthoclase; augite in twinned blades; dial- 
lage; titaniferous magnetite; brown alteration-product of 
angite; secondary quartz. Scale, 20 diameters. 
Fig. 2.—Another portion of the same section in polarized light, much 
enlarged. Orthoclase; labradorite; twinned augite; net- 
3 work of secondary quartz. Scale, 37 diameters. 
Fig. 3.—From Bohemian Mountain, near Lac La Belle, Keweenaw Point. 
N. E. 4, Sec. 32, T. 58, R. 29 W. Red-stained oligoclase 
and orthoclase; diallage altered to uralite; titaniferous 
magnetite and gray substance from its alteration; large 
apatites. Scale, 20 diameters. 
Fig. 4.—From Brunschweiler’s River, Wis. S. E. 7, Sec. 16, T. 45, R.4 W. 
Labradorite; orthoclase; titaniferous magnetite; augite; 
secondary quartz; apatite. In polarized light. Scale, 25 
diameters. 
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