74 
COPFER-BEARING ROCKS OF LAKE SUPERIOR. 
Tabulation of the results of a microscopic study of fine-grained olivinitic diabases (includ- 
ing melaphyrs)—Continued. 
Constituents as determined by 
microscope, in order of age. 
w 
] 
2 a Macroscopic char- 
g Place. 3 acters 
P : & 
g & 3 | 4 
i: o 5 D é 
: 2|3|8| 4 
a Se lala] & 
1875...| North shore Béte | SW. | 27 | 68 |28W.| Fine-grained, 
Grise Bay, Ke- greenish-black; 
weenaw Point, greasy; ‘‘lus- 
Michigan, near ter-mottled.” 
junction with 
Eastern Sand- 
stone. 
1884... Hillside above old | NW.| 31 | 58 |29W.| Medium-grained, 
smelting works, dark brownish- 
north side Lac gray; much- 
La Belle, Ke- weathered; 
weenaw Point, “luster-mot- 
Michigan. tlings,” not pro- 
nounced. 
1919...) Road from Lac La | SW. | 30 | 58 |}29W.| Black to dark 
Belle to Dela- brownish- gray; 
ware Mine, Ke- fine-grained; 
weenaw Point, “luster-mot- 
Michigan. tled.” 
2597...| Porcupine Mount- | SW. | 17 | 51 |42W.| Fine-grained, 
ains, Michigan. brownish-gray. 
81 W1..| Potato River, 17 | 46 |1W.| Very fine-grained, 
Ashland Coun- luster-mottlings 
ty, Wisconsin. of minute green- 
ish spots one- 
twentieth inch 
in diameter, 
surrounded by 
brown altera- 
tion-product. 
Olivine, very abundant, and 
wholly altered to a green sub- 
stance with brown and red 
stripes and crowded with the 
magnetite into the interspaces 
of the augites; anorthite, fresh, 
tabular, small; magnetite ; 
augite in the characteristic 
areas. 
Olivine, wholly altered to green 
substance with dark-brown 
streaks and patches, crowded 
between the augites; anorth- 
ite; magnetite, not abundant; 
augite, quite fresh, in the 
usual large areas, including 
many feldspars. 
Olivine, in rounded grains, very 
abundant, and crowded be- 
tween the augites, wholly 
altered to a greenish and 
brownish substance; thelarge 
amount of ochre-staining 
seeming to indicate an olivine 
rich in iron; anorthite; mag- 
netite ; augite, very fresh, in 
the usual large areas. 
Olivine, wholly altered to green- 
ish substance with red bands; 
anorthite; magnetite; augite, 
predominant, mostly fresh, 
but partly altered to viridite, 
in the usual large areas; 
chlorite pseud-amygdules. 
Olivine, wholly altered: plagio- 
clase, fresh; augite, fresh. 
1R. Pumpelly, Geology of Wisconsin, Vol. III, pp. 38, 41, 42. 
Angle between 
maximum ex- 
tinctions of 
adjacent hemi- 
tropic bands of 
the plagioclase 
in sections cut 
at random in 
the zone O: ti. 
Angles on| 2 
osite oe 
sides of| 4¢ 
cross-hair.| & © 
° ° ° 
32 33 65 
30 31 61 
21 23 44 
22 26 48 
34 32 66 
32 31 63 
32 29 61 
