76 
COPPER-BEARING ROCKS OF LAKE SUPERIOR. 
Tabulation of the results of a microscopic study of fine-grained olivinitic diabases (includ- 
ing melaphyrs)—Continued. 
Angle between 
maximum ex- 
tinctions of 
} adjacent hemi- 
2 tropic bands of 
5 2 | : : ; the plagioclase 
3 Plice: g | Macroscopic char- | Constituents as determined by in sections cut 
5 = acters. microscope, in order of age. at random in 
| 3 a. | the zone O: Zz. 
g é :|2 Angl 2 
E 2123/2] & opposite | 23 
2 5 SIS 8 ides of |S EI 
na SC \lnla| & eross-hair.| & 
° ° ° 
568....| North shore Lake | NE. | 16 | 51 |12 W.| Fine-grained, dark | Olivine, wholly altered to green 
Superior, be- gray, very pro- and brown substance, crowd- 
tween the nounced lumpy ed into the interspaces with 
mouthsof French fracture result- the magnetite; plagioclase ; 
and Sucker ing from the| magnetite; augite, fresh, 
Rivers, Minne- | deeper weather-| greatly predominating in 
sota. | ingoftheaugite| large areas. 
| interspaces. 
605.--.| North shore Lake | NE. | 29 | 51 |11 W. Greenish-gray,fine | Olivine, wholly altered to green | 35 31 66 
| Superior, one, grained, minute-| substance, abundant; anor-| 32 | 37 | 69 
mile below ; | ly ‘‘luster mot-| thite; magnetite; augite, very 
month of Knife tled.” fresh, in large areas, includ- 
River, Minne- ing great numbers of the tab- 
| sota. ular feldspars. A very typi- 
cally developed ‘‘luster-mot- 
| tled” rock. 
| 628....| North shore Lake NE. | 11 | 52 11W.| Fine-grained; dark | Olivine, wholly altered to green 
| Superior, south purplish-gray; substance with red bands; 
point of Agate “lustre-mot-| plagioclase too much altered 
Bay, Minnesota. tling” not pro- for measurement; magnetite ; 
| nounced. augite, fresh, predominant, 
} in the usual large areas; chlo- 
| = 
| | rite pseud-amygdules. 
660....) North shore Lake | NW.) 22 | 53 |10W. Very fine-grained, | Olivine, wholly altered to brown | 34 36 70 
Superior, from 5 greenish- black, substance; anorthite; magne- | 33 32 65 
feet dike, below semi-conchoidal| fite; augite,inthe usual large | 32 32 64 
mouth of Silver fracture, areas. An excessively fine- | 31 31 62 
| Creek, Minne- grained rock. 
sota. 
688....| North shore Lake | NE. | 27 | 54 | 9 W.| Very fine-grained; | Olivine, wholly altered to red | 27 31 58 
Superior, 3 of a rough fracture; substance, as usual in the | 27 29 56 
mile above v.16 light brown. interspaces with the magne-| 26 | 33 | 59 
mouth of Goose- tite; labradorite: magnetite: 
berry River, augite, very fresh, and in the 
Minnesota. usual relatively large areas, 
including many feldspars; 
but in this rock the ‘‘luster- 
mottling’ is wholly micro- 
scopic. 
696....| North shore Lake | NE. | 23 | 54 | 9W.| Fine-grained; | Olivine, in very abundant and | 31 37 68 
Superior, 2 altered; mottled unusually minute particles, | 32 35 67 
miles above the red and light; largely altered to green and | 34 27 61 
mouth of Split gray. red substances; magnetite; | 33 32 65 
Rock River, anorthite; augite, very fresh | 29 33 62 
Minnesota. in the usual areas. ‘31 33 64 
: | 
