ORTHOCLASE-BEARING GABBRO. 5S 
the S. E. 4, Sec. 32, T. 48, R. 12 W., Douglas County, Wisconsin. Other 
instances are the coarse gray rock of the Saint Louis River bluffs at and 
near Duluth, Minn.; the exposures in the woods west of Lester River, Min- 
nesota, in Sec. 29, T.51, R.13 W.; the rock exposed in the bed of Cascade 
River, in the southern half of See. 10, T. 62, R. 2 W.; the rock of the south 
side of Eagle Mountain, about four miles north of the last-named place; 
and the rock forming the west wall of the gorge through which the trail 
passes from Eagle Mountain to Brulé Lake. 
Tabulation of observations on orthoclase-bearing gabbros. 
Angle between 
maximum ex- 
tinctions of 
adjacent hemi- 
“ tropic bands of 
o : the plagioclase 
a ince a Macroscopic char- | Constituents as determined by in sections cut 
5 , 3 acters. microscope, in order of age. at random in 
a 3 - the zone O: 72. 
| a oa 
2 E Fi rales Angles on | & 6 
cs Bis E = opposite | og 
& Bae (Soul) wes sides of | Sg 
n Clalal wa eross-hair. | = 
° ° ° 
1902 | Bohemian Mount- | NE, | 32 | 58 |29W.| Medium - grained | Apatite, abundant, often quite | 14 17 31 
ain, north side to coarse-grain- large crystals; oligoclase and | 11 13 24 
Lac la Belle, Ke- ed; mixture of orthoclase, both reddened and 4 si 11 
weenaw Point, red feldspars dulled; titaniferous magne- 2 4 6 
Michigan. and shining dark tite; augite; diallage, mostly | 20 18 38 
greenish - black altered to uralite; amorphous 4 5 9 
mineral. green substance, secondary to | 15 12 27 
augite; gray substance sec- 
ondary to titaniferous magne- 
tite; a little secondary quartz. 
Bed 94! Eaglo River sec- | SE. | 30 | 58 !31W. Medium - grained | Apatite ; oligoclase ; orthoclase ; 22 
tion, Keweenaw to coarse; black, titaniferous magnetite; augite; 23 
Point, Michigan. thickly studded a little altered magma ; sec- 31 
with long red ondary ferrite, chlorite, quartz, 33 
feldspars. Sp. from the feldspars ; secondary 33 
gr., 2.94, yellowish-green mineral and 33 
magnetite, from the augite. 36 
6 W. | Old Ironton trail, | N. 4} 34 | 46 |1W.| Coarse-grained, | Plagioclase; orthoclase, highly 
Ashland County, red, black, and altered, much stained with 
Wisconsin. gray mottled; ferrite ; titaniferous magnetite, 
shows much coarse and abundant; diallage 
highly - magnet- largely altered to wralite ; chlo- 
ite. Sp. gr.,2.89. rite secondary to the feldspars ; 
magnetite, secondary to dial- 
lage; alittle secondary quartz. 
1 Metasomatic Development of the Copper-bearing Rocks of Lake Superior, Proc, Am. Acad. Sci., Vol. XU, pp. 253-309, 
