CORPEIG SILVER EIN S Ole iE EKA DiS ERICA, 357

number of small pores. The groundmass consists of small,
rounded grains of epidote in a mesh of fine actinolite needles.
The amphibole is a dull grayish-green color in hand specimens
and in thin section is a pale, slightly bluish-green with an indis-
tinct pleochroism. It has a marked fibrous structure with pos-
itive elongation, negative double refraction, and an extinction on
the fibers of 10 to 20 degrees.

Adjoining the ore shoots, the rocks contain, in addition, gar-
net, a little quartz, more hematite and magnetite, and a dark-
greenish calcite apparently colored by a fine network of actinolite
fibers.

Under the microscope no other minerals were seen. The epi-
dote, which forms about 50 per cent. of the rock, or more, occurs
as phenocrysts about 2 or 3 millimeters in length, and also as a
close aggregate of small round grains a fraction of a millimeter
in diameter. The fibrous hornblende is not so plentiful as in the
rock farther from the shoots, and does not occur as phenocrysts
but forms a large portion of the groundmass. Grains of quartz
were observed in the sections filled with fine, hair-like crystals of
actinolite. The garnets are the next most plentiful mineral after —
hornblende. They form grains several millimeters in diameter
showing a slightly yellowish color, and always a strong anomalous
double refraction. Magnetite, like calcite, is a late mineral and
is found in veins cutting through the rock and as crystals in open
vugs.

The Ore-——The ore occurs in shoots, extending across the beds
almost at right angles, and often penetrating the adjoining beds.
They have flat, elliptic outlines, with the major axis vertical,
when sectioned perpendicular to the bedding, and have an aver-
age width of about 6 feet. Their size is, however, somewhat
variable and they are not regularly spaced. They are shown in
Fig. 48.

The centers of the shoots are composed of a band of almost
solid bornite irregularly replacing the epidote more or less com-
pletely for a width of several inches. The limits of these bands
are not clearly defined, the bornite simply becomes more sparsely