86 
COPPER-BEARING ROCKS OF LAKE SUPERIOR. 
Tabulation of the results of a microscopic study of diabase-porphyrite and ashbed-diabase 
—Continued. 
Place. 
Macroscopic char- 
Composition as determined by 
Angle between 
maximum ex- 
tinctions of 
adjacent hemi- 
tropic bands of 
the plagioclase 
in sections cut 
at random in 
7 
3 Fi 
3 2 acters. the microscope. thezonetOeen 
a @ & penne cal 
° a 5s | a oO 
5 \glal¢ “opposits| 38 
a 5s |8/6| 4 sides of | 43 
& @lelale cross-hair.| & © 
7 ° ° ° 
() South side of Aphanitic; dark | Tabular plagioclase for the most 
Michipicoten chocolate-brown ; part, with the longer axes in 
Island. conchoidal frac-| a common direction, the crys- 
ture; no por- tals minute, but still several 
phyritic ingredi-| times largerthan in No. 4, pre- 
ents. dominating ; magnetite in not 
abundant small particles; 
qugite inminute grains; some 
residuary magma. 
?) | Copper mine, Like No. 4of Mich- | The base of this rock is much 
Michipicoten ipicoten collec-| like that of No.4 of this col- 
Island. tion. lection. In it are rare but 
quite large (#; to } inch across) 
erystals of augite, largely 
changed to a greenish ma- 
terial, but with cores of fresh 
augite remaining. 
(8) | Southeast corner Matrix aphanitic; | Base:—light and dark brown, | 10 14 | 24 
Michipicoten greenish - gray; unindividualized material, 
Island. very abundant producing little or no effect 
porphyritic between the crossed nicols; 
white feldspars, this is thickly studded with 
ysto finch long; minute plagioclases and holds 
also, rarer and rarer and more minute black 
much more mi- particles of magnetite. Por- 25 24 49 
nute black por- phyritic ingredients :—very |.4 [32 o7 59 
phyritie parti- abundant, large-sized, and E 29° 30 59 
cles. very fresh labradorite, several fF Gi 21 42 
crystals often clustered in an 
interesting way; also augite, 
much smaller and rarer, com- 
monly much altered to green- 
ish material and asseciated 
with magnetite. 
aT eeesas OO reaaciactaae Matrixaphanitic; | Close to preceding, differing |4 (46! 99 36 
dark brownish- only in having much red ma- E}i0 19 35 
gray; very terial in the base and the feld- 
abundant pink spars somewhat decomposed 
porphyritic and dulled. Figs. 1 and 2 of 
| feldspars, aver- Plate IX. represent this sec- 
| aging yy inch in tion. 
| length. SiOz, 
| 60.89 per cent. 
1 Macfarlane’s Michipicoten Collection, No.5, ‘‘Melaphyr.”’ 3Macfarlane’s Michipicoten Collection, No. 16, ‘‘Porphyrite.” 
?Macfarlane’s Michipicoten Collection, No.9, ‘‘Melaphyr.”’ 4Macfarlane’s Michipicoten Collection, No. 17, ‘‘Porphyrite.” 
