Dodgeville chronicle. [volume] (Dodgeville, Wis.) 1862-current, 1871-08-18
MINING DEPARTMENT.

may have stated before, if so [ will re-
peat it here, that in order to obtain correct
and comprehensive knowledge of min eral
viens, and the deposits of ore In those
veins. we must become acquainted not only
with the different forms of deposit, but with
the physical condition, or forces that have
produced them.
In the forms of deposit already referred
to, we recognize very distinctly the action
of physical forces with which we are famil-
lar forces that are still at work, slowly but
surely wearing down our hills, washing
away our soil, and filling up our vallies.
These forces have been at work since dry
land first appeared, and will continue to
work until every valley shall be exalted,
and every hill shall be made low.
There is another form of deposit however
that we meet with very near the surface,
and even sometimes at the surface, that we
cannot regard as the work of the agencies
referred to above; but that seems to be the
work of another and very different class
of agencies. The nature and form OF this
deposit, indicates the direction of the forces
to be from below, and not from above as in
the case of the other deposits.
The peculiar features of this form of de-
posts are as follows: The ore is found in
a basin shaped depression on the surface of
the rock. And this is not in the vallies, but
usually on high ground. Above the ore the
depressioas is usually filled with coarse
clay, sometimes mixed with what the n1in-
ers call tumbling rock. 1t is the same
character of rock, as the sides of the de-
preston, and is doubtless the result of ex-
tensive decomposition that has taken place
in the rock in the place. The origin per-
hsps of the basin shaped depression there.
IN connection with the ore, and usually
forming it's matrlx, is layer of clay of the
finest texture, called by the miners soap
clay. Its extreme fineness and greasy
touch, resembles very much, tallow that
has been melted and allowed to cool. This
kind Of clay seems to accompany ore always
in this form of deposit.
| The ore itself is usually found not far
| above the rock, the floor of which is very
uneven, and looks as though it had been
attacked by strong acids, Or eaten out by
powerful solvents. The arrangement of
the ore is sometimes very similar to what
it is in what is called fat openings, found
at considerable depth in the rock, with
even the accompaniment OF ocher, and calc
spar. At other times it is found in larger
detached masses, weighing from few
pounds, to several tons. There are instances
in our lead district, where masses OF lead
ore have been found, in this form Of deposit,
weighing from Is to 20 tons and the whole
deposit yielding from two to three million
pounds.
The rock which these deposits rest carry
all the features Of what is called good min
eral bearing rock. 1t is often fisSured ex-
sively; or as is sometimes the case in the
absence of many assures, chimneys are
found extending into the underlying strata
And what is very remarkably, we find
assures or seems, in the everything
clay assures too with bearings following
the direction of the assures in the rock
below. This would indicate that the con-
ditions necessary co the formation of these
deposit, had been in operation since the
clay in those depressions had been formed,
consequently the deposit was formed, at
or near the surface. hence found there in
its normal condition.
Between this form of deposit, and in the
one produced by the wearing down of hills,
with their mineral contents, and re-depos-
ting the material in the bottoms of valleys,
there is a very striking difference. They
are evidently the results of very different
physical conditions. One has had Mechan-
zeal, the ether a Chemical origin. The one
has been produced by atmosphe ,ic agencies,
or physical forces acting from above; the
other by physical forces, and condition
that we must seek now to discover.
These are some of the changes and
notifications that have been going on
in the crust of the earth, through vast
cycles of time, under the influence of GER
tain physical forces, and conditions that
have at last wrought out its present shape
To look at those changes, and notifications,
even with wonder and admiration, may be
the work of the listless, and untutorcd,
but to arrange and classify them, and to
seek their relation to natural laws, and
physical conditions that under,ie them
as their cause, is the work before us, and
upon which we shall enter in our next.
j. MURRIsH,