Nature and Character of Mineral Veins—Metalliferous Deposits—Mines—Their
Drainage and Ventilation—Their Depth—Diffusion of the Metals—Gold—
Silver—Lead—British Mines—Quicksilver—Copper—Tin—Cornish Mines—Coal—
Iron—Most abundant in the Temperate Zones, especially in the Northern—
European and British Iron and Coal—American Iron and Coal—Arsenic and
other Metals—Salt—Sulphur—Diffusion of the Gems.
THE tumultuous and sudden action of the volcano and the earthquake on
the great masses of the earth is in strong contrast with the calm,
silent operations on the minute atoms of matter by which Nature seems to
have filled the fissures in the rocks with her precious gifts of metals
and minerals, sought for by man from the earliest ages to the present
day. Tubal-cain was “the instructor of every artificer in brass and
iron.” Gold was among the first luxuries, and even in our own country,
from time immemorial, strangers came from afar to carry off the produce
of the Cornish mines.[91]
The ancients scarcely were acquainted with a third of the thirty-five
metals now known, and the metallic bases of the alkalis only date from
the time of Sir Humphry Davy, having formed a remarkable part of his
brilliant discoveries.[92]
Minerals are deposited in veins or fissures of rocks, in masses, in
beds, and sometimes in gravel and sand, the detritus of water. Most of
the metals are found in veins; a few, as gold and tin, iron and copper,
are disseminated through the rocks, though rarely. Veins are cracks or
fissures in rocks, seldom in a straight line, yet they maintain a
general direction, though in a zigzag form, striking downwards at a very
high angle, seldom deviating from the perpendicular by so much as
forty-five degrees, and extending to an unfathomable depth. They are for
the most part accompanied by a subsidence of the strata on one side of
their course, and by an elevation on the other; the throw, or
perpendicular distance between the corresponding strata on the opposite
sides of a vein, varies from a few inches to thirty, forty, even a
hundred fathoms. The beginning or end of a vein is scarcely ever known;
but, when explored, they are found to begin abruptly, and, after
continuing entire to a greater or less distance, they branch into small
veins or strings.
In the downward zigzag course of a vein, the bending of the strata
upwards on one side and downwards on the other, and the chemical changes
almost always observed on the adjacent rocks, veins bear a strong
analogy to the course and effects of a very powerful electrical
discharge.
Veins have been filled with substances foreign to them, which have
probably been disseminated in atoms in the adjacent rocks or by
sublimation. Nothing can be more certain than that the minute particles
of matter are constantly in motion from the action of heat, mutual
attraction, and electricity. Prismatic crystals of salts of zinc are
changed in a few seconds into crystals of a totally different form by
the heat of the sun: casts of shells are found in rocks, from which the
animal matter has been removed, and its place supplied by mineral
matter; and the excavations made in rocks diminish sensibly in size in a
short time if the rock be soft, and in a longer time when it is hard—
circumstances which show an intestine motion of the particles, not only
in their relative positions, but in space, which there is every reason
to believe is owing to electricity—a power which, if not the sole agent,
must at least have co-operated essentially in the formation and filling
of mineral veins.[93]
The magnetism of the earth is presumed to be owing to electrical
currents circulating through its surface in a direction at right angles
to the magnetic meridians. Mr. Fox, so well known in the scientific
world, has long since shown, from observations in the Cornish mines,
that such currents do flow through all metallic veins. Now, as the
different substances of which the earth is composed are in different
states of electro-magnetism, and are often interrupted by non-conducting
rocks, the electric currents, being stopped in their course, act
chemically on all the liquids and substances they meet with. Hence, Mr.
Fox has come to the conclusion that not only the nature of the deposits
must have been determined by their relative electrical conditions, but
that the direction of the metallic veins themselves must have been
influenced by the direction of the magnetic meridians; and, in fact,
almost all the metallic deposits in the world are in parallel veins or
fissures tending from east to west, or from north-east to south-west.
Veins at right angles to these are generally non-metalliferous, and, if
they do contain metallic ores, they are of a different kind. In some few
cases both contain the same ore, but in very different quantities, as in
the silver-mine at Pasco, in the Andes, and both veins are richer near
the point of crossing than elsewhere.
Sir Henry de la Beche conceives that the continued expansion and
elevation of an intensely heated mass from below would occasion numerous
vertical fissures through the superincumbent strata, within which some
mineral matters may have been drawn up by sublimation, and others
deposited in them when held in solution by ascending and descending
streams of water; but even on this hypothesis the direction of the rents
and the deposition of the minerals would be influenced by the electrical
currents. But if veins were filled from below, the richest veins would
be lowest, which is not the case in Cornwall, Mexico, or Peru.[94] The
primum mobile of the whole probably lies far beyond our globe: we must
look to the sun’s heat, if not as the sole cause of electrical currents,
at least as combined with the earth’s rotation in their evolution.[95]
When veins cross one another, the traversed veins are presumed to be of
prior formation to those traversing, because the latter are dislocated
and often heaved out of their course at the point of meeting; and such
is the case with the metalliferous veins, which are therefore the most
recent. Veins are rarely filled in every part with ore; they contain
sparry and stony matter, called its matrix, with here and there
irregular masses of the metallic ores, often of great size and value.
Solitary veins are generally unproductive, and veins are richer when
near one another. The prevalence and richness of mineral veins are
intimately connected with the proximity or junction of dissimilar rocks,
where the electro-molecular and electro-chemical actions are most
energetic. Granite, porphyry, and the plutonic rocks are often eminently
metalliferous; but mineral deposits are also abundant in rocks of
sedimentary origin, especially in and near situations where these two
classes of rocks are in contact with one another, or where the
metamorphic structure has been induced upon the sedimentary. This is
remarkably the case in Cornwall, the north of England, in the Ural, and
all the great mining districts.
The metalliferous deposits are peculiar to particular rocks: gold and
tin are most plentiful in granite and the rocks lying immediately above
it; copper is deposited in various slate formations resting on the
preceding, and in the trias; lead is found in the mountain-limestone
system, and is rare where iron and copper abound; iron abounds in the
coal and oolitic strata, and in a state of oxidule and carbonate in the
older rocks; and silver is found in almost all of these formations; its
ores being frequently combined with those of other metals, especially of
lead and copper. There is such a connection between the contents of a
vein and the nature of the rock in which the fissure is, that, when in
the oldest rocks the same vein intersects clay-slate and granite, the
contents of the parts enclosed in one rock differ very much from what is
found in the other. It is believed that in the strata lying above the
coal-measures none of the more precious metals have been found in
England in such plenty as to defray the expense of raising them,
although such a rule does not extend to the continent of Europe or to
South America, where copper and silver ores abound in our new red
sandstone series. In Great Britain no metal is raised in any stratum
newer than the magnesian limestone. Metals exist chiefly in the primary
and early secondary strata, especially near the junction of the granite
and slates; and it is a fact that rich veins of lead, copper, tin, &c.,
abound only in and near the districts which have been greatly shaken by
subterraneous movements. In other countries, as Auvergne and the
Pyrenees, the presence of igneous rocks may have caused mineral veins to
appear in more recent strata than those which contain them in Great
Britain.
When a mine is opened, a shaft like a well is sunk perpendicularly from
the surface of the ground, and from it horizontal galleries are dug at
different levels according to the direction of the metallic veins, and
gunpowder is used to blast the rocks when too hard for the pickaxe. When
mines extend very far in a horizontal direction, it becomes necessary to
sink more shafts, for ventilation as well as for facility in raising the
ore. Such is the perfection of underground surveying in England, that
the work can be carried on at the same time from above and below so
exactly as to meet; and in order to accelerate the operation, the shaft
is worked simultaneously from the different galleries or levels of the
mine. In this manner a perpendicular shaft was sunk 204 fathoms deep,
about nineteen years ago, in the Consolidated mines in Cornwall; it was
finished in twelve months, having been worked in fifteen different
points at once. In that mine there are ninety-five shafts, besides other
perpendicular communications under-ground from level to level: the depth
of the whole of these shafts added together amounts to about 25 miles;
the galleries and levels extend horizontally about 43 miles, and 2500
people are employed in it: yet this is but one of many mines now in
operation in the mining district of Cornwall alone.[96]
The infiltration of the rain and surface-water, together with
subterranean springs and pools, would soon inundate a mine and put a
stop to the work, were not adequate means employed to remove it. The
steam-engine is often the only way of accomplishing what in many cases
would otherwise be impossible, and the produce of mines has been in
proportion to the successive improvements in that machine. In the
Consolidated mines already mentioned there are nine steam-engines
constantly pumping out the water; four of these, which are the largest
ever made, together lift from thirty to fifty hogsheads of water per
minute, from an average depth of 230 fathoms. The power of the
steam-engines in draining the Cornish mines is equal to 44,000 horses—
one-sixth of a bushel of coals performing the work of a horse. The
largest engine is between 300 and 350 horse-power; but as horses must
rest, and the engine works incessantly, it would require 1000 horses to
do its work.[97]
Mines in high ground are sometimes drained to a certain depth by an adit
or gallery dug from the bottom of a shaft in a sloping direction to a
neighbouring valley. One of these adits extends through the large mining
district of Gwennap, in Cornwall; it begins in a valley near the sea,
and very little above its level, and goes through all the neighbouring
mines, which it drains to that depth, and with all its ramifications is
30 miles long. Nent Force Level, in the north of England, forms a
similar drain to the mines in Alston Moor: it is a stupendous aqueduct 9
feet broad, and in some places from 16 to 20 feet high; it passes for
more than 3 miles under the course of the river Nent to Nentsbury
engine-shaft, and is navigated underground by long narrow boats.
Daylight at its mouth is seen like a star at the distance of a mile in
the interior. Most of the adits admit of the passage of men and horses,
with rails at the sides for wagons.
The ventilation of mines is accomplished by burning fires in some of the
shafts, which are in communication with the others, so that currents of
air flow up one and down the others. In some cases fresh air is carried
into the mines by streams that are made to flow down some of the shafts.
Were this not done, the heat, which increases with the depth, would be
insupportable; ventilation diminishes the danger from the fire-damp,
for, even where Sir Humphry Davy’s safety-lamp is used, accidents happen
from the carelessness of the miners.[98]
The access to deep mines, as in Cornwall, is by a series of
perpendicular or slightly inclined ladders, sometimes uninterrupted, but
generally broken at intervals by resting-places. It is computed that
one-third of a miner’s physical strength was exhausted in ascending and
descending a deep mine: they are now drawn up by the steam-engine.
The greatest depth to which man has excavated is nothing when compared
with the radius of the earth. The Eselschacht mine at Kuttenberg in
Bohemia, now inaccessible, which is 3778 feet below the surface, is
deeper than any other mine. Its depth is only 150 feet less than the
height of Vesuvius, and it is eight times greater than the height of the
pyramid of Cheopos, or the cathedral of Strasburg. The Monkwearmouth
coal-mine near Sunderland, descends to 1500 feet below the level of the
sea, so that the barometer stands there at 31·80, which is higher than
anywhere on the earth’s surface.[99] The salt-works of New Saltzwerk in
Prussia are 2231 feet deep, and 1993 feet below the level of the sea;
and various other mines, such as the Liege coal-mine of Esperance, and
that of Mont Massi, in the Maremma of Tuscany, do the same. Mines on
high ground may be very deep without extending to the sea-level: that of
Valenciana, near Guanaxuato in Mexico, is 1686 feet deep, yet its bottom
is 5960 feet above the surface of the sea; and the mines in the higher
Andes must be much more. For the same reason the rich mine of
Joachimsthal in Bohemia, 2120 feet deep, has not yet reached that level.
The fire-springs at Tseu-lieu-tsing in China are 3197 feet deep, but
their relative depth is unknown.[100] How insignificant are all the
works of man compared with nature!—A line 27,600 feet long did not reach
the bottom of the Atlantic Ocean.
The metals are very profusely diffused over the earth. Few countries of
any extent do not contain some of them. A small number occur pure, but
in general they are in the form of ores, in which the metal is
chemically combined with other substances, and the ore is often so mixed
with earthy matter and rock that it is necessary to reduce it to a
coarse powder in order to separate the ore, which is rarely more than a
third or fourth part of the mass brought above ground.
Gold is found in almost every country, but in such minute quantities
that it is often not worth the expense of working. It is almost always
in a native state, and in the form of crystals, grains, or rolled
masses. Sometimes it is combined with silver. It is exhausted in several
parts of Europe where it was formerly found. The united produce of the
mines in Transylvania, Hungary, the north-western districts of Austria,
and the bed of the Danube, is nearly 60,000 ounces annually. Gold is
found in small quantities in Spain, in the lead-hills in Scotland, and
the Wicklow mountains in Ireland.
Gold abounds in Asia, especially in Siberia. The deposits at the foot of
the Ural mountains are very rich. In 1826 a piece of pure gold weighing
23 pounds was found there, along with others weighing three or four
pounds each, together with the bones of elephants. All the diluvium
there is ferruginous; and more to the east, as already mentioned, a
region as large as France has lately been discovered with a soil rich in
gold-dust, resting on rocks filled with it. In 1834 the treasures in
that part of the Altaï chain called the Gold Mountains were discovered,
forming a mountain-knot nearly as large as England, from which a great
quantity of gold has been extracted. Gold is found in Tibet, in the
Chinese province of Yun-nan, and abundantly in the mountains of the
Indo-Chinese peninsula, in Japan, and Borneo. In the latter island it
occurs near the surface in six different places.
Africa has long furnished a large supply to Europe. That part of the
Kong Mountains west of the meridian of Greenwich is one of the most
auriferous regions in the world. The gold stratum lies from 20 to 25
feet below the surface, and increases in richness with the depth. It is
found in particles and pieces in a reddish sand. Most of the streams
from the table-land bring down gold, as well those that descend to the
low ground to the north, as those that flow to the Atlantic. On the
shores of the Red Sea it was found in sufficient quantity to induce the
Portuguese to form a settlement there.
In South America, the western Cordillera is poor in metals except in New
Grenada, where the most westerly of the three chains of the Andes is
rich in gold and platinum—a metal found only there, in Brazil, and on
the European side of the Ural mountains—in alluvial deposits. The
largest piece of platinum that has been found weighed 21 ounces. Gold is
found in sand and gravel on the high plains of the Andes, on the low
lands to the east of them, and in almost all the rivers that flow on
that side. The whole country between Jaen de Bracamores and the Guaviare
is celebrated for its metallic riches. Almost all the Brazilian rivers
bring down gold; and the mine of Gongo Socco, near Rio de Janeiro, is
said to yield several varieties of gold-ore. Central America, Mexico,
and California are auriferous countries. The quantity of gold recently
found near the surface in California is very great. [There is no
definite statement of the amount.] A considerable quantity is found in
Tennessee, the mountains of Georgia, and on 1000 square miles of North
Carolina it occurs in grains and masses.
A great deal of silver is raised in Europe. The mines of Hungary are the
most productive, especially those in the mountains of Chemnitz. The
metalliferous mountains of the Erzgebirge are also very rich, as also
the mines near Christiania in Sweden. Silver is also found in Saxony,
Transylvania, and Austria. In no part of the old continent is silver in
greater abundance than in the Ural and Altaï mountains, especially in
the district of Kolywan. There are silver-mines in Armenia, Anatolia,
Tibet, China, Cochin-China, and Japan.
The richness of the Andes in silver can hardly be conceived, but the
mines are frequently on such high ground that the profits are diminished
by the difficulty of carriage, the expense of living in a barren
country, sometimes destitute of water, where the miners suffer from the
cold and snow, and especially the want of fuel. This is particularly the
case at the silver-mines of Copiapo in Chile, where the country is
utterly barren, and not a drop of water is to be found in a circuit of
nine miles. These mines were discovered by a poor man in 1832, who hit
upon a mass of silver in rooting out a tree. They extend over 150 square
leagues. Sixteen veins of silver were found in the first four days, and,
before three weeks elapsed, forty more, not reckoning smaller
ramifications, were discovered. The rolled pieces which lay on the
surface produced a large quantity of pure silver. A single mass weighed
5000 pounds.[101]
In Peru there are silver-mines along the whole range of the Andes, from
Caxamarea to the confines of the desert of Atacama. The richest at
present are those of Pasco, which were discovered by an Indian in 1630.
They have been worked without interruption since the beginning of the
seventeenth century, and seem to be still inexhaustible. The soil under
the town of Pasco is metalliferous, the ores probably forming a series
of beds contemporaneous with the strata. The richness of these beds is
not everywhere the same, but the nests of ore are numerous. The mines of
Potosi, 16,150 feet above the sea-level, are celebrated for riches, but
the owners have to contend with all the difficulties which such a
situation imposes. The small depth at which the silver lies on the high
plains of the Andes, and the quantity of it on the surface, is probably
owing, as has been already stated, to the greater deposition of the
sublimed mineral from refrigeration near the surface. The ore in the
mines at Chota is near the surface over an extent of half a square
league, and the filaments of silver are sometimes even entwined with the
roots of the grass. This mine is 13,300 feet above the level of the sea,
and even in summer the thermometer is below the freezing-point in the
night. In the district of Huantajaya, not far from the borders of the
Pacific, there are mines where masses of pure silver are found, of which
one weighed 800 pounds.[102]
According to Baron Humboldt, the quantity of the precious metals brought
to Europe between the discovery of America and the year 1803 was worth
1257 millions sterling; and the silver alone taken from the mines during
that period would form a ball 89 feet in diameter. The disturbed state
of the South American republics has interfered with the working of the
mines.
Lead-ore is very often combined with silver, and is then called
Argentiferous Galena. It is one of the principal productions of the
British mines, especially in the northern mining district, which
occupies 400 square miles at the junction of Northumberland, Cumberland,
Westmoreland, Durham, and Yorkshire. It comprises Alstan Moor, the
mountain-ridge of Crossfell, and the dales of Derwent, East and West
Allen, the Wear, and Tees. There are other extensive mining tracts
separated from this by cultivated ground. The principal products of this
rich district are lead and copper. The lead-mines lie chiefly in the
upper dales of the Tyne, Wear, and Tees, and all of it contains more or
less silver, though not always enough to indemnify the expense of
refining or separating the silver. The deleterious vapours resulting
from this process are conveyed in a tube along the surface of the ground
for 14 miles; and instead of being, as formerly, a dead loss to the
proprietor, they are condensed in their passage, and in one instance
yield metal to the annual value of 10,000_l._[103] The Hudgillburn
lead-mine in that district has yielded treasures almost unexampled in
the annals of mining. The veins, from ten to twelve, and in some places
even twenty feet wide, were filled with ore which is entirely obtained
with the pickaxe, without blasting. In 1821 the galena of this mine
yielded 32,000 ounces of silver.
Lead-mines are in operation in France, but not to any great amount:
those of the south of Spain furnish large quantities of this metal; also
in Saxony, Bohemia, and Carinthia, where they are very rich. Lead is not
very frequently found in Siberia, though it does occur in the Nerchinsk
mining district, in the basin of the river Amur. It is also a production
of China, of the peninsula beyond the Ganges, and of America. It is also
found in Lower Peru, Mexico, and in California, where the richest
argentiferous lead is worked.
[The northwest country, or Upper Mississippi Valley, is among the most
remarkable in the world for the variety and abundance of its mineral
deposits, and especially for those which are of most extensive use in
the arts. The sulphuret of lead occupies about one degree of latitude,
extending north from a point on the Mississippi, about eight miles below
Galena, and lying on both sides, varying in width, till it covers as
great an extent from east to west. On the east side of the river the
lead-ore is found principally in a clay matrix, at a depth of sometimes
only five or six feet from the surface; on the west side of the river it
runs at the depth of one hundred feet or more, overlaid with magnesian
limestone. To the south-west of the lead deposit is a very abundant bed
of iron, about forty miles long by twenty-five broad. The copper region
extends north from the lead deposits to Lake Superior; it embraces about
three hundred square miles. To the south of the lead region is a vast
bed of bituminous coal of good quality, at no great distance below the
surface.
In the mineral district there are about four thousand persons employed
in digging lead-ore. The value of the lead annually produced is
estimated at $1,500,000. A considerable quantity, in form of pig-lead,
is exported to China.]
Quicksilver—a metal so important in separating silver from its ores, and
in other arts as well as in medicine—occurs either liquid in the native
state, or combined with sulphur in that of cinnabar. It is found in the
mines of Idria and some other places in the Austrian empire, in the
Palatinate on the left bank of the Rhine, and in Spain. The richest
quicksilver mines of Europe, at the present day, are those of Almaden,
where the quicksilver is found in the state of sulphuret chiefly. These
mines were worked 700 years before the Christian era, and as many as
1200 tons of the metal are extracted annually. It occurs in China,
Japan, and Ceylon, at San Onofro in Mexico; and in Peru, at
Guancavelica, the mines of which, now almost deserted, produced, up to
the beginning of the present century, the enormous quantity of 54,000
tons of quicksilver. The discovery of quicksilver mines in California
has been announced.
Copper is of such common occurrence that it would be vain to enumerate
the localities where it is found. It is produced in Africa and America,
in Persia, India, China, and Japan. The Siberian mines are very
productive both in ore and native copper. Malachite is the most
beautiful of the ores, and the choicest specimens come from Siberia.
Almost every country in Europe yields copper. The mines in Sweden,
Norway, and Germany are very productive; and it forms a principal part
of our own mineral wealth. It is raised in all the principal mining
districts in England and Wales. In Cornwall it is very plentiful, and is
often associated with tin. The period at which the Cornish mines were
first worked goes far beyond history, or even tradition: certain,
however, it is that the Phœnicians came to Britain for tin. Probably
copper was also worked very early in small quantities, for its
exportation was forbidden in the time of Henry VIII. It was only in the
beginning of the eighteenth century that the Cornish copper-mines were
worked with success, in consequence of the invention of an improved
machine for draining them.[104]
[On the lands south of Lake Superior is a body of copper ore, supposed
to be the richest in the world. It is almost pure in some specimens: so
that, as taken from the earth, it was wrought into church utensils by
some of the French who first visited the place; and a portion of the
large rock deposited on the grounds of the War Department, at
Washington, has been polished so as to present the appearance of
sheet-copper.
At a recent meeting of the “American Association for the Advancement of
Science,” held at Cambridge, Mass., August 1849, Mr. J. S. Hodge,
speaking of the mineral region of Lake Superior, said:—“The mines are
wrought wholly for native copper. The veinstone with scattered
particles, furnish what is called _stamp work_; which is crushed under
heavy stamps and then washed; the lumps are called _barrel ore_, being
packed in barrels for transportation; and the masses, after being cut up
into pieces not exceeding two tons in weight, are shipped in bulk. The
size of some of these masses is so enormous as almost to exceed belief.
They have been broken up in the Cliff mine of 60 and even 80 tons in
weight. Such pieces are reduced, in the mine, to fragments of seven tons
weight and less, and after being hoisted to the surface are still
further reduced.
“At the Minesota mine, near the Ontonagon river, I had an opportunity of
examining, in June, the most extraordinary mass yet met with. Two shafts
had been sunk on the line of the vein 150 feet apart. At the depth of
about 30 feet they struck massive copper, which lay in a huge sheet with
the same underlay as that of the vein—about 55° towards the north.
Leaving this sheet as a hanging wall, a level was run under it
connecting the two shafts. For this whole distance of 150 feet the mass
appears to be continuous, and how much further it goes on the line of
the vein either way there is no evidence, nor beside to what depth it
penetrates in the solid vein. I examined it with care, striking it
repeatedly with my hammer in order to detect, if possible, by the sound,
any break or interruption there might be in the mass—for a thin scale of
stone encrusted it sometimes and concealed the face of the metal.
Examinations had been made by drilling through this scale, where it
attained the thickness of an inch or so; but in no place had any sign of
a break been found. It forms the whole hanging wall of the level,
showing a width of at least eight feet above the floor in which its
lower edge was lost. It had been cut through in only one place, where a
partial break afforded a convenient opportunity. Measuring the thickness
here as well as the irregular shape of the gap admitted, it was found
somewhat to exceed five feet. Assuming the thickness to _average_ only
one foot, there would be in this mass 1200 cubic feet, or about 250
tons—still it is not safe to assume even one foot, for the masses vary
extremely in thickness.
“The mode adopted to remove these masses is to cut channels through them
with cold chisels, after they are shattered by large sand blasts put in
behind them. Grooves are cut with the chisels across their smallest
places, one man holding, and another striking, as in drilling. A chip of
copper three-quarters of an inch wide, and up to six inches in length,
is taken out, and the process is repeated until the groove passes
through the mass. The expense of this work is from eight to twelve
dollars per superficial foot of the face exposed. Fragments of veinstone
enclosed in the copper prevent the use of saws. A powerful machine,
occupying little room, is much needed, which would perform more
economically this work.
“The greatest thickness of any mass cut through at the Cliff Mine has
been about three feet. Their occurrence through the vein is not regular.
Barren spots alternate with productive portions. The same is the case in
all the mines. The total product of the Cliff Mine for the year 1848 is
estimated at 830 tons, averaging 60 per cent. During the present year
more than half this amount has been already sent down, and there is
enough more on the surface and in sight in the mine to warrant the
belief that 1000 tons will be the product of the year’s work, or 600
tons of copper. The whole amount of copper annually imported into the
United States is about the value of two million dollars, or about 5400
tons. But little has been supplied from our own mines. Nine such mines,
then, as the Cliff, would render us independent of foreign supplies.
From present appearances, after careful examination of the region, and
consideration of the progress made in mining since my last visit in
1846, I feel myself warranted in expressing a decided conviction that
this amount of copper must be supplied in very few years, and this metal
soon become, as lead already has, one of export instead of import. The
recent failures of mining speculations, wildly undertaken, and
ignorantly and extravagantly conducted, may for a time check the
development of these mines; but their wonderfully rich character is now
beginning to be properly appreciated, as well as the reliance which may
be put in the surface-appearance of the veins. Some curious features in
their character and distribution have been detected, which have
heretofore escaped observation for want of sufficient data, and which
will, I believe, be found of great consequence in the selection of the
best localities. These, after farther examination, I may at another time
make public. The history of these mines, so far, has remarkably proved
the foresight and excellent judgment of the lamented Dr. Houghton,
particularly so in his predictions of the disastrous effects that must
result from such speculations as have caused the country to be overrun
by hordes of adventurers.
“The silver found associated with the copper has not proved of much
importance, perhaps for the reason that the greater part of it is
purloined by the miners. The Cliff Mine has probably yielded more than
thirty thousand dollars worth, of which not more than a tenth part has
been secured by the proprietors. I saw myself, the present season, no
less than six pounds and eight ounces of lumps and bars of silver seized
in the hands of an absconding workman.”]
In Cornwall clay-slate rests upon granite, and is traversed by
porphyritic dykes. The veins which contain copper or tin, or both, run
east and west, and penetrate both the granite and the clay-slate. The
non-metalliferous veins run north and south; and if veins in that
direction do contain any metal, it never is tin or copper, but lead,
silver, cobalt, or antimony, which with little exception are believed to
be always in the clay-slate. No miner in Cornwall has ever seen the end
or bottom of a vein; their width varies from the thickness of a sheet of
paper to 30 feet; the average is from one to three feet. It rarely
happens that either tin or copper is found nearer the surface than 80 or
100 feet. If tin be first discovered, it sometimes disappears after
sinking the mine 100 feet deeper, when copper is found, and in some
instances tin is found 1000 feet deep without a trace of copper; but if
copper is first discovered, it is very rarely succeeded by tin. Tin is
found in rolled pieces, in horizontal beds of sand and gravel, and is
called stream-tin. The most valuable tin-mines on the continent of
Europe are those in Saxony; it also occurs in France, Bohemia, and
Spain. One of the richest deposits of tin known is in the province of
Tenasserim, on the east side of the gulf of Martaban, in the Malayan
peninsula. These deposits occur in several parts of that country; the
richest is a layer eight or ten feet thick of sand and gravel, in which
masses of oxide of tin are sometimes the size of a pigeon’s egg. The
best of all comes from the island of Banca, at the extremity of the
Malacca peninsula; a large portion of it is imported into Britain, and
much goes to China. It is found in the alluvial tracts through every
part of the island, rarely more than 25 feet below the surface. Great
deposits occur also in the Siberian mining district of Nertshinsk, near
the desert of the Great Gobi, and in Bolivia, near Oruro.
There are comparatively few coal-mines worked within the tropics; they
are mostly in the temperate zones, especially between the Arctic Circle
and the Tropic of Cancer; and as iron, the most useful of metals, is
chiefly found in the carboniferous strata, it follows the same
distribution. In fact, the most productive iron-mines yet known are in
the temperate zones. In the eastern mining district of Siberia, in the
valley of the river Vilui, the ores are very rich, and very abundant in
many parts of the Altaï and Ural. In the latter, the mountain of Blagod,
at 1534 feet above the sea, is one mass of magnetic iron-ore.[105] Coal
and iron are worked in so many parts of Northern China, Japan, India,
and Eastern Asia, that it would be tedious to enumerate them.
In Europe the richest mines of iron, like those of coal, lie chiefly
north of the Alps. Sweden, Norway, Russia, Germany, Styria, Belgium, and
France, all contain it plentifully. In Britain many of the coalfields
contain subordinate beds of a rich argillaceous iron-ore,
interstratified with coal, worked at the same time and in the same
manner; besides, there is a substratum of limestone, which serves as a
flux for melting the metal. The mines lie near Birmingham, on the
northeast frontier of the great coal-basin of South Wales, near
Pontypool and Merthyr Tydvil. There are extensive iron-mines in
Staffordshire, Shropshire, North and South Wales, Yorkshire, Derbyshire,
and Scotland. Altogether there are about 220 mines, which yield iron
sufficient for our own enormous consumption, and for exportation. These
productive mines would have been of no avail had it not been for the
abundance of fuel with which the greater part of them in the north of
England, Scotland, and Wales are associated—the great source of our
national wealth, more precious than mines of gold. Most of the
coal-mines would have been inaccessible but for the means which their
produce affords of draining them at a small expense. A bushel of coals,
which costs only a few pence, in the furnace of a steam-engine generates
a power which in a few minutes will raise 20,000 gallons of water from a
depth of 360 feet—an effect which could not be accomplished in a shorter
time than a whole day by the continuous labour of twenty men working
with the common pump. Yet this circumstance, so far from lessening the
demand for human labour, has caused a greater number of men to be
employed in the mines.[106]
The coal strata lie in basins, dipping from the sides towards the
centre, which is often at a vast depth below the surface of the ground.
The centre of the Liege coal-basin is 21,358 feet, or 3-1/2 geographical
miles deep, which is easily estimated from the dip, or inclination, of
the strata at the edges, and the extent of the basin. The coal lies in
strata of small thickness and great extent. It varies in thickness from
3 to 9 feet, though in some instances several layers come together, and
then it is 20 and even 30 feet thick; but these layers are interrupted
by frequent dislocations, which raise the coal-seam towards the surface.
These fissures, which divide the coalfield into insulated masses, are
filled with clay, so that an accumulation of water takes place, which
must be pumped up.
There are three immense coalfields in England. The first lies north of
the Trent, and occupies an area of 360 square miles; and although the
quantity of coal annually raised in Northumberland and Durham amounts to
a million and a half of tons, there is enough to last 1000 years. London
is chiefly supplied from it. The second or central coalfield, which
includes Leicester, Worcester, Stafford, and Shropshire, has an area of
1495 square miles, and supplies the manufactories round it, and the
midland counties south and east of Derbyshire. The third or western
coalfield includes South Wales, Gloucestershire, and Somersetshire. The
coalfield of South Wales alone is 100 miles long, and 18 or 20 broad.
The Workington and Whitehaven coal-mines go a mile under the sea;
several shafts in the latter are 100 fathoms deep; and it is one of the
finest in England for extent and thickness of strata, some of the seams
being nine feet thick.
The Scotch coal-measures occupy the great central low-land of Scotland,
lying between the southern high lands and the Highland mountains; the
whole of that rude tract is occupied by them, besides which there are
other coalfields of less extent. Coal has been found in seventeen
counties in Ireland, but the island contains only four principal coal
districts—Leinster, Munster, Connaught, and Ulster. Thus, there is coal
enough in the British islands to last some thousands of years; and were
it exhausted, our friends across the Atlantic have enough to supply the
world for ages uncountable. Moreover, if science continues to advance at
the rate it has lately done, a substitute for coal will probably be
discovered before our own mines are worked out.[107]
The carboniferous strata are enormously developed in the States of North
America. The Appalachian coalfield extends, without interruption, 720
miles, with a maximum breadth of 280 miles, from the northern border of
Pennsylvania to near Huntsville, in Alabama, occupying an area of 63,000
square miles. It is intersected by three great navigable rivers—the
Monogahela, the Alleghany, and the Ohio—which expose to view the seams
of coal on their banks. The Pittsburgh seam, 10 feet thick, exposed on
the banks of the Monogahela, extends, horizontally, 225 miles in length
and 100 in breadth, and covers an area of 14,000 square miles, so that
this seam of coal may be worked for ages almost on the surface, and in
many places literally so. Indeed, the facility is so great, that it is
more profitable to convey the coal by water to New Orleans, 1100 miles
distant, than to cut down the trees with which the country is covered
for fuel, and which may be had for the expense of felling. The coal is
bituminous, similar to the greater part of the British coal; forty miles
to the east, however, among the ridges of the Appalachian chain, there
is an extensive outlying member of the great coalfield, which yields
anthracite, a species of coal which has the advantage of burning without
smoke.
In the western States, the Illinois coalfield, which occupies part of
Illinois, Indiana, and Kentucky, is as large as England, and consists of
horizontal strata, with numerous seams of rich bituminous coal. There is
a vast coalfield also in Michigan. Large areas in New Brunswick and Nova
Scotia abound in coal. Iron is worked in many parts of the States, from
Connecticut to South Carolina.[109]
The tropical regions of the globe have been so little explored that no
idea can be formed of the quantity of coal or iron they contain; but as
iron is so universal, it is probable that coal is not wanting. It is
found in Formosa. Both abound in Borneo, and in various parts of
tropical Africa and America. There is comparatively so little land in
the southern temperate zone, that the mineral produce must be more
limited than in the northern, yet New Holland, Van Diemen’s Land, and
New Zealand are rich in coal and iron.
Arsenic, used in the arts and manufactures, is generally found combined
with other metals in many countries as well as our own. Manganese, zinc,
bismuth, and antimony are raised to a considerable amount. As the
qualities of the greater part of the more rare metals are little known,
they have hitherto been interesting chiefly to the mineralogist.
The mines of rock-salt in Cheshire seem to be inexhaustible. Enormous
deposits of salt extend 600 miles on each side of the Carpathian
mountains, and throughout wide districts in Austria, Gallicia, and
Spain. It would not be easy to enumerate the places in Asia where
rock-salt has been found. Armenia, Syria, and extensive tracts in the
Punjab abound in it, also China and the Ural district; and the Andes
contain vast deposits of rock-salt, some at great heights.
Volcanic countries in both continents yield sulphur. Sicily, where it is
found in the tertiary marine strata, unconnected with the volcanic
district, is the magazine which supplies the greater part of the
manufactures of Europe. It is often found beautifully crystallized.
Asphalt, nitre, alum, and naphtha are found in various parts of Europe
and Asia, and natron is procured from small lakes in an oasis on the
west of the Valley of the Nile.
The diffusion of precious stones is very limited. Diamonds are mostly
found in a soil of sand and gravel, and in the beds of rivers. Brazil
furnishes most of the diamonds in commerce; they are the produce of
tracts on each side of the Sierra Espenhaço, and of a district watered
by some of the affluents of the Rio San Francesco. During the century
ending in 1822, diamonds were collected in Brazil to the value of three
millions sterling, one of which weighed 138-1/2 carats. The celebrated
mines of Golconda have produced many splendid diamonds; they are also
found in Borneo, which produced one weighing 367 carats, valued at
269,378_l._ The eastern parts of the Thian-Tchan, on the great platform
of Asia, and a wide district of the Ural Mountains, yield diamonds.
The ruby and sapphire have the same crystalline form, and are nearly
allied to corundum; both are found in Ceylon, in the gravel of streams.
The rubies at Gharan, on the verge of the river Oxus, are found imbedded
in limestone. The gravel of rivulets in the Birman empire contains the
oriental, star, and opalescent rubies. The spinelle also occurs in that
country in a district five days’ journey from Ava. The Hungarian rubies
are of inferior value. The blue, green, yellow, and white sapphires are
the produce of the Birman empire, and the spinelle is not uncommon in
Brazil.
The finest emeralds come from veins of clay-slate in the valley of Musa,
in New Grenada. Beryls are found in Brazil, and in the old mines in
Mount Zabarah, in Upper Egypt. Those of Hungary and of the Heubach
Valley, near Saltzburg, are very inferior in colour and quality.
Hungary and Bohemia yield the finest opals; the most esteemed are
opaque, of a pale brown, and shine with the most brilliant iridescence;
some are white, transparent, or semi-transparent, and radiant in
colours: the precious opal is found in Hungary and in Mexico. The most
beautiful garnets come from Bohemia and Hungary; they are found in the
Hartz mountains, Ceylon, and many other localities. The turquoise is a
Persian gem, and supposed to be the fossilized enamel of the tooth of a
fossil mastodon; it is also found in Tibet and in the Belat-Tagh in
Badakshan, which is the country of the lapis lazuli, mined by heating
the rock, and then throwing cold water upon it. This beautiful mineral
is also found in several places of the Hindoo Coosh, in the hills of
Istalif north of Cabool, in Tibet, and in the Baikal mountains in
Siberia.
The cat’s-eye is peculiar to Ceylon; the king of Kandy had one two
inches broad. Topaz, beryl, and amethyst are of very common occurrence,
especially in Brazil, Siberia, and other places. They are little valued,
and scarcely accounted gems. Agates are so beautiful on the table-land
of Tibet, and in some parts of the desert of the Great Gobi, that they
form a considerable article of commerce in China; and some are brought
to Rome, where they are cut into cameos and intaglios. But the greater
part of the agates, cornelians, and chalcedonies used in Europe are
found in the trap-rocks of Oberstein, in the Palatinate.
Thus, by her unseen ministers, electricity and reciprocal action, the
great artificer Nature has adorned the depths of the earth and the heart
of the mountains with her most admirable works, filling the veins with
metals, and building the atoms of matter, with the most elegant and
delicate symmetry, into innumerable crystalline forms of inimitable
grace and beauty. The calm and still exterior of the earth gives no
indication of the activity that prevails in its bosom, where treasures
are preparing to enrich future generations of man. Gold will still be
sought for in the deep mine, and the diamond will be gathered among the
débris of the mountains, while time endures.