File:The Quarterly journal of the Geological Society of London (13958710603).jpg

1866.. BAUERMAN COPPER-MINES OF MICHIGAJT. 453
condary planes. The finest crystallized varieties are, as a rule, ob-
tained from the Ontonagon district, and generally are more abundant
in newly opened mines than in those which are worked at greater
depths.
In the Porcupine Mountains, to the west of the Ontonagon River,
a compact epidote rock is found containing copper in such a very
finely divided state, that it has hitherto been impossible to work it
advantageously. Native silver is found to a small extent, either
crystallized in arborescent forms, or irregularly spotted through the
copper, the line of separation between the two metals being well
marked in polished specimens. The Cliff" and Minnesota mines have
produced the largest amount of the precious metal, the absolute
production, however, being but small ; and scarcely any portion of
what is found comes into the hands of the mining adventurers,
except a few pounds which are annually got by hard picking from
the coarser sizes of the dressed mineral. The larger pieces find their
way into the hands of dealers and collectors, the earlier miners
having appropriated them to their own use, and the precedent has
been persistently followed ever since.
5. Distrihiition and Association of the Copper. — Among the three
classes of deposits in which the mines are worked, the most important
are the stratified amygdaloids, which will therefore be first considered.
They are confined to the district of which Portage Lake (an inlet
which nearly cuts the Peninsula into two parts) is the centre. The
oldest mines are on the southern or Houghton side of the lake, so
called from the town or village named after the geologist who
examined the country ; while the newer and more important ones
are on the northern side, above the village of Hancock. The banks
of the lake on either side rise steeply from the water to a height of
from 400 to 600 feet ; the dressing-fiows, being placed close to the
water, receive the ores from the mines (which are located on the high
tablelands above) by means of railways and inclined planes. Taking
the extreme north and south mines as limits, the district has a
length, measured along the strike of the trappean belt, of about 9
miles, and a breadth of from 3 to 5 miles. The general section,
showing the position of the copper-bearing beds, is as shown in
Fig. 1. The series of beds indicated are amygdalous traps, which con-
tain more or less copper in the cavities, and are regularly mined under
. Pig. 2. — Section from the Peiuahic Lode to the Albany and
Boston Conglomerate (530 feet).
Albany & I ^ . fll4#
PewabicLode, Old Pewabic Green Amygdaloid Boston ^-^45 ^(2 c 2« 
12 ft. Lode, 32 ft. Lode, 19 ft. Lode, 7 ft. p^3 w ^ S Q § ®
'J^Ml£^2y.d^^/^^
the name of " lodes." In the uppermost or Hancock series, only