122 COPPER-BEARING ROCKS OF LAKE SUPERIOR. 
Tabulation of the results of a microscopic examination of augite-syenites, &e.—Continued. 
Place. 
Specimen number. 
791and| North shore Lake 
787. Superior, Min- 
nesota, south 
point of Beaver 
Bay. 
Quarter-section. 
a 
Section. 
Township. 
Microscopic char- 
acters. 
SW.| Pale  flesh-red; 
medium to fine- 
grained; alarge 
proportion of 
therock appears 
to be made up of 
pinkish feld- 
spars. 
835. North shore of | NE. | 32 | 56 | 7W.| Medium-grained; 
Lake Superior, 
Minnesota. 
flesh-red; gran- 
ite-like; quartz 
and feldspars 
both plainly re- 
cognizable to the 
naked eye. 
Microscopic descriptions. 
The thin section is made up 
chiefly of much dulled and 
clouded feldspars, a few of 
which are obscurely banded. 
Quartz occurs in little par- 
ticles, filling corners, and in 
some few places is plainly 
secondary, but on the whole 
it is much less abundant in 
this section than in most of 
those previously described. |° 
There are areas in the section 
which present a cloudy, red- 
stained appearance, which 
may be either much altered 
feldspars or felsitic matrix. 
Magnetite is rather coarse 
and abundant for this class of 
rocks. 
The thin section is close to that 
of 762, consisting for the most 
part of coarse, turbid, pink- 
ish-stained feldspars and clear 
quartz. The feldspars show 
in large part a fine lineation 
in the polarized light, and 
give the low polarization 
angles of oligoclase. Proba- 
bly half of the feldspars are, 
however, orthoclase. The 
feldspar crystals are always 
of quite large size, measuring 
often one to two inches in 
width. The quartz is not so 
coarse, but still is in very 
large particles for this class 
of rocks, and enters the feld- 
sparin such a way as to ren- 
der certain its secondary ori- 
gin, or at least its deposition 
after the feldspars had be. 
come thoroughly eaten and 
honeycombed. There are one 
or two places in the section 
Angle between 
maximum ex- 
tinotionsof 
adjacent hemi- 
tropic bands of 
the plagioclase 
in sections cut 
at random in 
the zone O: iz. 
ee 
