130 COPPER-BEARING ROCKS OF LAKE SUPERIOR. 
Tabulation of microscopic observations upon sandstones, &e.—Continued. 
Macroscopic descrip- 
Place. tions. 
Microscopic descriptions. 
Specimen num- 
ber. 
Quarter-section. 
Section. 
Township. 
Range. 
Es 
-_ 
No 
oa 
a 
-| From the base of the NE. 31W.| Fine-grained; very | The larger particles of this rock are 
“Great Conglom- dark-red; firm. fragments worn from quartziferous 
erate" near Copper porphyries and augite-syenites, as in 
Falls, Keweenaw the two preceding rocks; except that 
Point, Michigan. the particles are smaller and the 
quartzes more abundant in this case. 
Thickly strewn among these larger 
particles are numerous smaller ones 
worn from basic rocks. These part- 
icles make up more than half the bulk 
of the rock, and to their presence the 
dark color is due. Much the larger 
proportion of these basic particles are 
fragments of magnetite, but there are 
also present numerous fragments of 
matrices of amygdaloids and of a 
nearly opaque red oxide of iron, which 
may be an alteration-product from 
some of the constituents of a basic 
tock. The latter particles are so 
opaque as to be readily mistaken for 
magnetite in the transmitted light. 
No infiltrated calcite is to be seen. 
1969.-' Sandstone of ‘‘Calu- |.......... 23 | 56 |383 W.| Fine-grained; dark- | Composed of coarser particles imbedded 
met conglomerate,” reddish; carries mi- in a matrix of fine particles, most of 
Calumet mine, nute red felsite peb- the former and all of the latter being 
Keweenaw Point, bles; effervesces highly angular. The larger particles 
Michigan. with hydrochloric consist chiefly of fragments of the 
acid. matrix and porphyritic feldspars of a 
quartziferous porphyry, along with 
which are rarer ones of amygdaloid 
matrix. The finer portion consists of 
the same materials with a larger pro- 
portion of basic detritus, abundant 
magnetite particles, rather plentiful 
quartz particles, and some infiltrated 
calcite and epidote. See Plate XVE, 
Fig. 4. 
| 1792..| Near the Atlantic NW. | 34 | 55 |34W.| Medium- to coarse- | Larger particles, running from 0.5™™ to 
mill, Portage Lake, grained; dark pur- 1.5™™ in greatest length, and angularto 
Michigan. plish-red, banded sub-angular—rarely much rounded— 
with light-red; some are imbedded in a matrix composed of 
portions effervesce fine particles. The larger particles, 
briskly, others not which tend to aggregate along certain 
at all. lines, are mostly of bubble-bearing 
quartz. There are also present among 
these larger particles pieces of red- 
dened and clouded feldspars, for the 
most part orthoclase, others of por- 
phyry matrix of the usual characters, 
ee 
