Specimen number. 
| 
| 
COPPER-BEARING ROCKS OF LAKE SUPERIOR. 
Place. 
1846 D | Pebble from Eagle | NW.) 19 
River conglom- 
erate, Keweenaw 
Point, Michigan. 
River conglom- 
erate, mouth of 
Eagle River, 
Keweenaw Point, 
Michigan. 
| 
Lama Pebble from the NW.) "| 55 = 
Albany and Bos- | 
ton conglomer. } 
ate, Keweenaw | 
Point, Michigan. | 
Macroscopic char- 
acters. 
Township. 
58 (31 W.) Finely crystalline; 
pinkish-gray; 
shows abundant 
feldspar facets 
and also dark 
greenish parti- 
evident feldspar 
Tabulation of the results of & microscopic examination of augite-syenites, &e.—Continued. 
Microscopic descriptions. 
Closely similar to the two pre- 
ceding. The still recognizable 
plagioclases are large and 
abundant, and some of them 
contain unmistakably the 
graphically arranged second- 
ary quartz. Irregularly out- 
lined augites, largely altered 
to ferrite, are not unfrequent. 
There is but little red stain, 
but ferrite needles of some 
size are rather abundant and 
always arranged in a sort of 
rude parallelism to the lines 
of the finer secondary, quartz. 
186A | Pebble from Eagle | NW.) 19 | 58 SI W.) Medium to fine) Made up chietiy of orthoclase 
grained; pink- 
ish; granite- 
and quartz, with rarer oligo- 
clases. There is very little 
quartz which from its ar 
rangement can be regarded as 
secondary, and none what- 
ever of the fine radiating 
quarts characteristic of the 
preceding rocks. A few 
large-sized clusters of red and 
black ferrite, associated with 
brightly polarizing particles, 
are seen; they are supposed 
to represent altered angites. 
Here and there calcite fills 
spaces between the other in- 
gredients. Though present 
ing some important differ 
ences from the previously de 
scribed sections, its mineral- 
ogical composition and gen- 
eral appearance are strongly 
suggestive of its close affinity 
tothem. It is a rather fine 
grained granite or granitell. 
Minutely orystal- | Clese to 183 A, 186i C, and 
line; dark-brown, 
mottled with) 
18460. In this section there 
isan evident gradation from 
the coarser graphically ar. 
ranged secondary quarts to 
the finer kinds; while coarse 
Angle between 
maximum ex- 
tinctions of 
ok 
Be 
3B 
