84 
COPPER-BEARING ROCKS OF LAKE SUPERIOR. 
Tabulation of the results of a microscopic study of diabase-porphyrite and ashbed-diabase— 
Continued. 
3 : 
z Place. E Mecracoric char. 
a = : 
a = | & 
E 2/8/38! ¢ 
3 a 1Si/E| a 
a 6 jalale 
on eine 
533....| Near mouth of |Sw.| 4 50 |13 W.| Very fine grained, 
Lester River, | but plainly erys- 
Minnesota. | talline; dark 
\ brownish gray; 
conchoidal frac- 
| / ture. 
547....| North shore of Sw. 34) 51/13 W.| Aphanitic; very 
Lake Superior, dense; dark) 
two miles below brown; rare mi- 
the mouth of nute porphyritic | 
Lester River, | feldspars. } 
Minnesota. | 
589....| North shore of | SW.| 31 | 51 | 11W.| Very fine-grained; 
Lake Superior, | light gray ; sub- 
one mile above | conchoidal frac- 
| themouthofthe ture. 
Knife River, 
Minnesota. 
655....| North shore of | NE. | 22 | 53 |10W.| Aphanitic; red- 
Lake Superior, dish brown; 
one mile below highly conchoid- 
the mouth of alfracture; car- 
Silver Creek, ries elongated 
foot of Encamp- amygdules of 
ment Bluff, Min- calcite. SiOz, 
nesota. } 60.03 per cent. 
712....| North shore of | West) 7| 54|8W.| Nearly aphanitic; | 
Lake Superior, | side. | indefinitely mot- 
| one-half mile) | tled red and 
north of Split | black, weathers 
Rock River, | bright red; very 
Minnesota. highly conchoid- 
| al fracture. 
797....| North shore of | SW.| 12 | 55|8W.| Veryfine-grained; 
Lake Superior, ; nearly black; | 
| Beaver Bay, conchoidal frac- 
| Minnesota. ture. 
884....| North shore of | SW.| 22 | 56 | 7W.| Nearly aphanitic; 
| Lake Superior, chocolate brown, 
bay above Great | conchoidal frac- 
Palisades, Min- ture. 
nesota, under- | 
lies the palisade | 
Tock. 
Constituents as determined by 
the microscope. 
. 
Oligoclase. predominates ; augite, 
grains not abundant; magne- 
tite; ferrite, abundant. 
Plagioclase; unindividualized 
substance; qaugite, in grains, 
not abundant; very abundant 
red and brown ferrite. 
Labradorite predominant, 
longer axes of crystals often 
incommon directions; magne- 
tite; augite in grains, abund- 
ant; afresh rovk. 
Groundmass :—oligoclase; much 
unindividualized substance, 
saturated with red ferrite; 
magnetite. Porphyritic in- 
gredients :—oligoclase; much 
altered augite. 
Oligoclase ; augite, abundant in 
grains; magnetite; ochre- 
stained, unindividualized sub- 
stance abundant, filling sharp- 
ly the spaces between the 
feldspars. 
Oligoclase ; augite in rounded 
particles very abundant, un- 
usually coarse for this class of 
rocks; magnetite. 
Plagioclase, predominant; unin- 
dividualized substance; rare 
minute grains of augite; mag- 
netite ; red ferrite completely 
saturating the entire section. 
Angle between 
maximum ex- 
tinctions of 
adjacent hemi- 
tropic bands of 
the plagioclase 
in sections cut 
at random in 
the zone O: it. 
14 i 25 
14 u 25 
9 6 15 
5 4 9 
2 13 23 
