1874.] Copper Mines of Lake Superior. 173 
copper permeating it, may have penetrated the pebble or 
been deposited around it,—it is difficult to say which. In 
the‘ conglomerate also occur boulders of solid copper. 
Some are said to exhibit a concentric arrangement of the 
copper, but one I had cut through the centre was homo- 
geneous in structure, but contained, embedded in the copper, 
a few crystals of quartz and felspar. 
Interstratified with the conglomerate are thin bands of 
copper sandstone, the copper being in fine grains, some- 
times deposited pure, at others mixed with. epidote and 
quartz or finely-ground porphyry, the laminz easily separable 
from one another. In their midst are sometimes embedded 
pebbles of copper. Bands of hard compact sandstone, from 
the disintegration of the same rock as compose the con- 
glomerate, are met with beneath the foot wall, on the hang- 
ing wall, or in the bed itself. A specimen in my possession 
exhibits successive layers firmly compacted, some of con- 
glomerate, others of coarse-grained and others of fine- 
grained sandstone, with a surface distin@tly ripple-marked. 
The aqueous origin of the bed cannot be doubted, but 
whether the copper was mechanically or chemically- de- 
posited, it is more difficult to decide. The easier expla- 
nation of its occurrence is on the hypothesis of a mechanical 
deposition, but, as militating strongly against it, is the un- 
doubted fact that the conglomerate pebbles very rarely carry 
copper. ‘The effects of subsequent chemical action are 
beautifully exhibited in a clay fluccan which, from the 
surface to nearly the lowest level driven, lines in places the 
foot-wall. In it, embedded in soft clay, derived from 
the disintegration of the rock, and which harden into 
amass that might almost be mistaken for a piece of trap, 
Occur with calc spar, laumonite, and quartz, copper in 
dendritic masses, distinctly crystallised. Some of the 
specimens taken from the fluccan undoubtedly exhibit 
instances of false crystallisation, plainly showing the 
impress of the crystals amidst which they were formed, but 
others are as undoubtedly themselves crystallised. Vugs 
also occur lined with crystals of epidote, and calc spar, and 
spongy copper; and through the bed there passes diagonally 
what is called a dropper. It is only a few inches wide, but 
consists of what is locally called brick copper, which is 
accompanied by crystallised silicated minerals, entangled in 
which are conglomerate pebbles. It has unmistakable 
slickensides, on which the copper is actually polished. 
A bed of amygdaloidal trap overlies the conglomerate, and 
is in places rich in copper. Some of the amyg edules are 
VOL. IV. (N.S.) Z 
