132 
COPPER-BEARING ROCKS OF LAKE SUPERIOR. 
Tabulation of microscopic observations upon sandstones, &c.—Continued. 
men num- 
ber. 
Speci 
2508..| Silver-bearing rock 
2535..| Bed of Upper Carp | 
-| Union mine lode, Por- 
] 
Place. 
underlying None- 
such vein, Porcu- 
pine Mountains, 
Michigan. 
cupine Mountains, | 
Michigan; top of 
sandstone underly- | 
ing “outer trap;” 
from bed of stream. 
River ; immediately 
overlying amygda- 
loid; Porcupine 
Mountains, Michi- 
gan. 
“4 1 Falls of Bad River, 
Ashland County, 
Quarter-section. 
Nw. 
Sw. 
| Section. 
19 
| Township. 
51 
51 
| Range. 
43 W. 
42 W. 
| Macroscopic descrip- 
tions. 
Very fine-grained; 
dark-gray; quartz- 
ite-like; firm and 
hard ; effervesces in 
places with hydro- 
chloric acid. 
Very fine-grained ; 
dark reddish-brown; 
firm;  effervesces 
readily with hydro- 
chloric acid. 
42W.| Excessively fine- 
grained; dark pnur- 
plish-red ; firm; ef- 
fervesces readily 
with hydro-chloric 
acid; finely banded 
with darker and 
lighter shades. 
3W.| Medium to coarse- 
grained; reddish. 
Si0., 69.78 per cent. 
Microscopic descriptions. 
calcite, and native copper, all of which, 
with the exception of the last named, 
are very irregularly distributed 
through the section. The copper 
molds itself sharply around the con- 
stituent fragments, having in most 
cases a core of magnetite, an occur- 
rence suggesting its precipitation by 
the ferrous oxide of the last-named 
mineral. The copperalso is occasion- 
ally to be seen penetrating into the 
interiors of the more readily decom- 
posable fragments. Plate XVI, Fig. 1. 
This rock is composed of predominant 
quartz fragments, with a smaller pro- 
portion of porphyry detritus, and a 
a large one—probably making up half 
the rock—of infiltrated quartz. There 
is also some infiltrated calcite, which 
is very irregularly distributed. 
A very fine-grained rock; much re- 
sembling 1792. Larger fragments of 
feldspar and porphyry matrix are im- 
bedded in a groundmass, composed of 
the same materials, with a large pro- 
portion of quartz. There is also 
present a notable proportion of basalt- 
ic detritus. The particles are for 
the most part quite angular. The 
interstices are everywhere filled with 
infiltrated calcite, along with some 
epidote. 
Very much like the last rock described, 
except that itis much finer in grain, 
and contains a small proportion only 
of basaltic detritus. 
Larger angular grains of quartz and 
feldspars are imbedded in a fine 
matrix composed of the same mate- 
Tials, along with much porphyry 
detritus, largely in a decomposed 
condition, and an abundant brown 
ocherous cement. 
oe mmm puonte 
