THE WAY INTO THE MINES.
A wise coal operator never begins to open a mine for the purpose of
taking out coal until he knows the character of the bed and the quality
of the mineral. This knowledge can only be obtained by an exhaustive
search for, and a careful examination of, all surface indications,
and by drilling or boring holes down to and through the strata of
coal. This is called “prospecting.” The examiner in a new field will
first look for outcrops. He will follow up the valleys and inspect
the ledges and the banks of streams. If he be so fortunate as to find
an exposure of the coal seams, or of any one of them, he will measure
its thickness, will calculate its dip and strike, and will follow its
outcrop. He will also study and make careful note of the rock strata
with which it is associated, for by this means he may be able to
determine the probability of other seams lying above or below it. This
examination of the rock strata he will make, whether coal is visible
or not visible. It will be of much service to him. For instance, it is
known that the great Baltimore vein in the Wyoming valley is usually
overlaid by a coarse red sandstone. If the examiner finds rock of this
character in that section, he has good reason to hope that coal lies
beneath it. Under the lowest coal seam of the anthracite beds there
is found, as a rule, a rock known as the conglomerate. If, therefore,
the explorer finds an outcrop of conglomerate, he will know that, as
a rule, he need not look for coal beyond it. This rock, coming to the
surface on the westerly side of the Moosic range of mountains, marks
the limit of the Lackawanna coal field toward the east. No one, having
once studied the conglomerate rock, could mistake it for any other,
though its composition is very simple. It is nothing more than white,
water-worn quartz pebbles, held together by a firm, lead-colored
cement. But it is a rock of unusual hardness and durability. It is
proof against the erosive action of water, grows harder by exposure
to the air, and has a consistency that approximates to that of iron.
In the coal districts it is used largely for building purposes, where
heavy walls and foundations are required. Experience has taught that
there are no coal seams below the conglomerate, so that wherever this
is found as a surface rock, or wherever it is pierced by the drill,
it is usually unnecessary to explore below it. If no coal outcrop is
found, the bed of a stream is searched for fragments of the mineral,
and, if any are discovered, they are traced to their source. Coal is
sometimes exposed where a tree has been uprooted by the wind, and
pieces of it have been found in the soil thrown out at a groundhog’s
burrow.
Wagon roads crossing the country may be scanned for traces of the
“smut” or “blossom.” This is the decomposed outcrop, which has become
mingled with the soil, and may be more readily distinguished in the
bed of a traveled road than elsewhere. Other surface indications
failing, the topographical features of this section of country should
be studied. Wherever the coal seams come to the surface, being softer
than the rock strata above and below them, they are disintegrated and
eroded more rapidly by the action of the atmosphere and the elements.
This wearing away of the exposed coal leaves the surface outline in
the form of a bench or terrace, which follows the line of the outcrop.
And this form is retained even with a thick deposit of soil over the
edges of the strata. Small shafts may be sunk or tunnels driven through
this thickness of earth, and the outcrop explored in this way. This
process of examination is of more value in the bituminous than in the
anthracite regions, since the bituminous coal, being soft, is more
rapidly eroded, and the terrace formation resulting from such erosion
is more distinct and certain. In these days, in the anthracite coal
fields, there is hardly an area of any great extent in which mines have
not been actually opened. These mines, therefore, in the facilities
they afford for studying exposed strata and developed coal seams,
offer the best means of acquiring knowledge concerning the coal beds
of adjoining tracts. In a country where no surface indications of coal
are found over a large area, it is hardly worth while to explore for it
by boring. In the anthracite regions of Pennsylvania the limits of the
coal beds are now so accurately defined that it is seldom necessary to
bore for the purpose of testing the presence of coal. But it is always
advisable, before opening a mine in a new field, to test the depth,
dip, and quality of the coal and the character of the seams by sinking
one or more bore holes. Surface measurements of a seam are, at best,
very uncertain, as indications of its continuing character. The angle
of dip may change radically before a depth of one hundred feet shall be
reached. And coal undergoes so great deterioration by long exposure to
the atmosphere that, in order to judge the quality of a coal bed, it is
necessary to have a specimen fragment from it that has been hidden away
in the rocks. Hence the necessity of boring.
Hand drills were generally used in the early days of prospecting, and
a sand pump drew out the sludge or borings for examination. This was
superseded by the spring pole method, which in turn gave way to the
rope method in use in the oil regions, the borings in each case being
carefully preserved for inspection. The diamond drill is the one now
in common use in the coal regions. Its cutting end is in the form of a
circle set with black, amorphous diamonds. It cuts an annular groove in
the rock as it descends, forming a core, which is withdrawn with the
drill, and which may be examined in vertical section. The sludge is
washed out by a stream of water which passes down through the centre of
the drill rod, and is forced back to the surface between the rod and
the face of the bore hole. The invention of this rotary cutting drill
is due to Leschot of Geneva, and the method of flushing the hole to
Flauvelle.
After having obtained all possible information concerning his coal
property, and, if he be wise, embodying it in the form of maps, the
coal operator must decide where he shall make an opening for mining
purposes, and what kind of an opening he shall make. The answers to
these two questions are, to a certain extent, dependent on each other,
as certain kinds of openings must be located at certain places. When
coal was first gathered for experiment or observation, it was taken
up loosely from the ground, where it had fallen or been broken down
from the outcrop of some seam. As it came into demand for practical
purposes, it was quarried from this outcrop backward and downward, as
stones for building purposes are now quarried, the seam being uncovered
as the work proceeded. This process was followed along the line of the
outcrop, but excavations were not made to any considerable depth, owing
to the great expense of uncovering the coal.
The open quarry system of mining coal has been successfully practiced
in America in but a few places. One of these was the great Summit
Hill open mine, near Mauch Chunk, where the Lehigh coal was first
discovered. Here, on a hill-top, was a horizontal coal bed, some
sixty acres in extent, and varying in thickness from fifteen to fifty
feet. Over this was a covering of rock, slate, and earth from three
to fifteen feet in thickness. This bed was mined by simply removing
the covering and taking the coal out as from a quarry. Other examples
of this method are seen at Hollywood Colliery, and at Hazleton No. 6
Colliery, both near Hazleton, in Luzerne County. There are isolated
instances of this method of stripping elsewhere in the anthracite
regions, but as a rule the conditions are not favorable for it.
Ordinarily there are four methods of making an entrance into a mine
for the purpose of taking out coal. These are known as the drift, the
tunnel, the slope, and the shaft.
To the early miners the drift was the favorite mode of entry. Finding
an exposed seam of coal in the face of a ledge or cliff, they would
dig in on it and bring the coal out from the opening in wheelbarrows.
A place was selected, if possible, where a creek or river ran at
the base of the ledge, and the coal was dumped from the wheelbarrow
directly into a boat. In default of a water way a wagon road was built
at the foot of the hill or cliff, a platform extended out over it, and
the coal was thus loaded from the wheelbarrow into the wagon.
[Illustration: CROSS SECTION OF DRIFT OR GANGWAY WITH TIMBERS AND
LAGGING.]
The modern drift, though fashioned on an improved plan, is the simplest
and least expensive way of making an entrance into a coal mine. The
outline of the proposed opening is first marked out on the edge of the
exposed coal seam. From fifteen to eighteen feet is an ordinary width
to accommodate two tracks, and ten feet will readily accommodate one.
Seven feet is an average height, though, if the seam be comparatively
flat, the coal will be taken down until the rock is reached, even
though a greater height should be attained. With this width and height
the opening is cut into the hill through the coal seam. The floor of
the drift must have a constant upward grade as it progresses inward, in
order that the water may run out, and that loaded cars may be hauled
more easily. The mouth of the drift must be above the level of the
adjacent valley or stream, so that the water may be carried away, and
the drift is therefore what is known as a water-level opening. It is
usually necessary to support the roof and sides of the drift by timbers
joined together in the form of a bent, and placed more or less closely
to each other. These timbers are also sometimes lined by sticks placed
behind and over them horizontally, and known as “lagging.” It will be
seen that the conditions under which the opening by drift may be made
place a serious limitation on the use of this method. It will also
now be seen why the drift is the simplest and most economical mode of
making an entrance to a mine. In this method there is no expense for
removing earth or for cutting through rock, nor any cost at any time of
pumping water or of hoisting coal. When the fact is remembered that it
sometimes costs from $50,000 to $100,000 to sink a deep shaft through
hard rock, and that to this amount must be added the cost of buildings,
machinery, and repairs, and the perpetual cost of pumping water and of
hoisting coal, the economy of the drift method will be appreciated. But
the day of drift mining in the anthracite regions has gone by. Those
portions of the coal beds lying above water level have been largely
mined out, and the areas of coal that are now accessible by drift are
very limited. In the bituminous districts, however, where the seams lie
comparatively flat and the coal is mostly above water level, the method
by drift is still almost universally used.
Next to a drift, the tunnel is the simplest and most economical method,
under certain circumstances, of making an entrance into a mine. This
is a passage driven across the measures, and at right angles to the
seam, in order to reach coal which at the point of opening is not
exposed. The tunnel is usually driven into the side of a hill. The
earth is first dug away until the rock is exposed, or, if the soil be
too deep for that, only enough of it is taken to make a vertical face
for the mouth of the tunnel. The opening is then driven into the hill
at about the same width and height that a drift would be made, and in
practically the same manner. If there is a section of earth tunneling
at the mouth, the timbering must be close, and the lagging will be of
heavy planks. When the solid rock is reached, however, it is not often
that any timbering is necessary, the sides and roof being so hard and
firm as not to need support. This passage is driven against the face
of a coal seam, and when the coal is finally reached the tunnel proper
ends, a passage is opened to the right and one to the left along the
strike of the seam, and from these gangways the coal is mined. The
tunnel, like the drift, must be above water level, and its floor must
have a descending grade toward the mouth, to carry off water. The
expense of the tunnel, and its superiority to the slope or shaft, will
depend upon the distance through which the rock must be pierced before
coal is reached. It is especially advisable, therefore, before opening
a tunnel, to have an accurate map of the location and dip of the coal
seams to be struck by it, otherwise no approximate calculation can be
made of the extent or cost of the work.
In the anthracite districts, where the seams are sharply pitching,
tunnels are driven in the interior of a mine from the workings of
a seam already opened across the intervening measures to strike an
adjacent seam. In this way two, three, or more coal seams can be
worked, and the coal can all be brought out at one surface opening.
This is virtually the only kind of tunneling that is now done in the
anthracite regions; for, as has already been explained, the coal that
lay above water level and was thus accessible by tunnel has now been
mostly mined out.
If there is an outcrop of coal on the tract to be mined, and the dip
of the seam is more than twenty degrees, it is usually advisable to
enter the mine by means of a slope. This is a passage which, beginning
at the outcrop, follows the coal seam down until the necessary depth
is reached. It is driven in the coal. The distinction between the
drift and the slope is that the drift is driven from the surface on
the strike of the seam while the slope is driven on its dip. Where
the coal seam comes within a moderate distance of the surface, as at
an anticlinal ridge, a slope may be driven through the rock until the
coal is reached at the axis, and from that point follow the seam down.
Sometimes a shaft is sunk to the top of an anticlinal ridge, and from
its foot two slopes are driven, one down each side of the roll, in
opposite directions. If the seam is very irregular, or if it is much
broken by faults, there may be a great deal of rock cutting to be done
in order to preserve the uniformity of grade necessary for the slope.
The cost may, indeed, in this case, amount to more than would have been
sufficient to sink a shaft to the same depth, although, as a rule, the
entrance by slope should cost only about one fourth of that by shaft.
[Illustration: CROSS SECTION OF SLOPE WITH DOUBLE TRACK.]
The same methods are employed in sinking a slope as are used in driving
a drift, except that generally the timbering need not be so heavy. The
minimum height of the slope is about 6½ feet, the width at the top, or
collar, about 8 feet, and the width at the bottom, or spread, about 12
feet. If a double track is desired the spread should be 18 feet and
the collar 14 feet. In the Wyoming region, where the dip is usually
less than twenty degrees, with infrequent outcrops, the slope is not in
general use; but in the Southern coal field, where the dip varies from
twenty degrees to the vertical, the slope is the most common method of
entering a mine. There the opening is driven down for a distance of 300
feet, at which point gangways are started out to right and left, along
the strike, and chambers driven from them back toward the surface. This
is called the first lift. The slope is then continued downward for
another distance of 300 feet, new gangways and chambers are laid off,
and this is called the second lift. This process is continued until the
synclinal basin is reached.
Where the dip of the slope is less than thirty degrees the coal is
brought to the surface in the car into which it was first loaded in the
mine. At a greater angle than this the ordinary mine car is superseded
by a car or carriage especially adapted to carrying coal up a steep
incline.
Where there is no outcrop in the tract to be mined, and the coal
lies below water level, the best mode of making an entrance to it is
by shaft. In the Wyoming region, since the upper veins have been so
generally mined out, nearly all the openings are by shaft. The location
of the shaft at the surface should be such that when it is completed
its foot shall be at the bottom, or nearly at the bottom, of the
synclinal valley into which it is sunk. As will be more readily seen
hereafter, this is necessary in order to carry the water of the mine
to the foot of the shaft, to facilitate the transportation of coal
under ground, and to get room to open up the greatest possible working
area. The depth to which a shaft must be sunk depends on the seam to
be reached, and on the district in which it is located. At Carbondale,
in the northeasterly extremity of the Wyoming basin, the average depth
to the conglomerate or bed of the lowest coal seam is 250 feet. From
Scranton to Pittston it is from 500 to 600 feet. At Wilkes Barre it is
1,200 feet. It reaches its greatest average depth a mile northeast of
Nanticoke, where it is from 1,500 to 1,600 feet.
This will be the limit of depth for shafts in the Wyoming region. At
present the average depth is from 300 to 400 feet, and there are few
that are more than 800 feet deep. The red-ash vein to which most of
the shafts are now being sunk is, at Pittston in the middle of the
general basin, from 450 to 650 feet below the surface. In the southern
anthracite region the average depth of shafts is somewhat greater, the
maximum depth being reached in the vicinity of Pottsville, where the
Pottsville deep shafts are about 1,600 feet in depth.
In beginning to open a shaft a rectangular space is staked out on the
ground from four to eight feet wider and longer than the proposed
dimensions of the shaft; and the soil and loose stones are thrown out
from this larger area until bed rock is reached, which is usually done,
except in the river bottom lands, within a depth of twenty feet.
From this rock as a foundation a cribbing of solid timber, twelve
inches square, is built up to the surface on the four sides of the
opening to prevent the earth from caving in. Sometimes heavy walls of
masonry are built up instead of the timber cribbing, and though the
original cost is greater, the purpose is far better answered by the
stone curbing. When this has been completed, sinking through the rock
goes on by the ordinary process of blasting, plumb lines being hung at
the corners of the shaft to keep the opening vertical.
An act of the Pennsylvania legislature, approved June 30, 1885,
regulates the conduct of coal mining in the State so far as the safety
of persons employed in and about the mines is concerned. Former acts
are consolidated and revised in this, and new provisions are added.
By virtue of this act both the anthracite and bituminous coal fields
are divided into districts, each of which is placed in charge of
an inspector, whose duty it is to see that the provisions of the
law are carried out, and to make annual report to the Secretary of
Internal Affairs of such facts and statistics as the law requires
to be made. As there will be frequent occasion hereafter to refer
to various provisions of this act of assembly, it will be mentioned
simply as the act of 1885. The matter is brought up here in order
that the rules relating to the sinking of shafts, as laid down in the
act, may be referred to. These rules provide the manner in which the
necessary structures at the mouth of the opening shall be erected, what
precautions shall be taken to prevent material from falling into the
pit, how the ascent and descent shall be made, that all blasts during
the process of sinking shall be exploded by an electric battery, etc.
All these rules have but one object, the safety of the workmen.
The horizontal dimensions of the modern shaft average about twelve feet
in width by thirty feet in length. This space is divided crosswise,
down the entire depth of the shaft, into compartments of which there
are usually four. The first of these compartments is the pump way, a
space devoted to the pipes, pump-rod, and other appliances connected
with the pumping system. To this six feet in breadth is allowed. Then
come, in succession, the two carriage ways, each of which may be seven
feet wide, and, finally, the air passage through which the foul air is
exhausted from the mine, and to which ten feet is appropriated. The
partitions between these compartments are made of oak sticks six inches
square, called buntons. The ends of the buntons are let into the rock
sides of the shaft, and they are placed horizontally at a vertical
distance from each other of about four feet. These bunton partitions
are then closely boarded down the entire distance. The partition
between the hoisting compartment and the airway is not only boarded up,
but the boards are matched and are rabbeted together. It is necessary
to make as nearly air-tight as possible this way for the passage of
air, and where the edges of the boarding meet the rock sides of the
shaft the irregularities are carefully filled in with brick and mortar.
Fastened to the buntons at each side of each hoisting compartment
are continuous strips of hard wood, from four to six inches square,
reaching from the top of the shaft to its bottom. These are the
“guides.” To each side of the carriage, which raises and lowers men and
materials, is fastened an iron shoe, shaped like a small rectangular
box without top or ends. This shoe fits loosely on to the guide,
slides up and down it, and serves to keep the carriage steady while
it is ascending or descending. This invention is due to John Curr of
Sheffield, England, who introduced it as early as 1798. The ordinary
carriage consists of a wooden platform with vertical posts at the
middle of the sides united by a cross-beam at the top, and all solidly
built and thoroughly braced. The posts are just inside of the guides
when the carriage is in place, and are kept parallel to them by the
shoes already mentioned. To the middle of the cross-beam is attached
the end of a wire cable, from which the carriage is suspended, and by
which it is raised and lowered. On the floor of the platform, which
is planked over, a track is built uniform with the track at the foot
and head of the shaft, and continuous with it when the carriage is at
rest at either place. The mine car is pushed on to the platform of the
carriage and fastened there by a device which clings to the axle or
blocks the wheels.
[Illustration: VERTICAL SECTION AT FOOT OF SHAFT, WITH ASCENDING
CARRIAGE.]
At the mouth of the shaft and projecting into it are the “wings,”
“keeps,” or “cage rests,” which are pressed against the sides of the
shaft by the ascending carriage, but spring back into place underneath
it and support it while it is at rest. When the carriage is ready to
descend the wings are withdrawn by hand levers.
The safety carriage is now in general use in at least one hoisting
compartment of every shaft. This carriage is built of wrought iron
instead of wood; it has a bonnet or roof as a protection against
objects falling down the shaft, and it has safety clutches or dogs to
stop the carriage and hold it in place in case of accident by breaking
ropes or machinery. Operators are required by the act of 1885 to
provide safety carriages for the use of their employees, and also to
keep movable gates or covers at the mouth of each shaft to prevent
persons and materials from falling into the opening.
Where mining is done by shaft there is seldom any other way provided
for the passage of workmen in and out than the way by the carriage.
A small shaft for the admission of air is sometimes driven down to
the highest part of the seam, and ladders are placed in the opening
on which men may climb up and down, but these ladders are seldom used
save in an emergency. It is made obligatory upon operators, by the act
of 1885, to provide two openings to every seam of coal that is being
worked; these openings to be at least sixty feet apart underground,
and one hundred and fifty feet apart at the surface. The object of this
rule is to provide a way of escape for workmen in case of accident to
the main outlet.
It is seldom necessary, however, in these days, to sink a separate shaft
in order to comply with this provision of the law; the underground
workings of the mines having such extensive connections that often not
only two but many openings are accessible from each seam.
As to the comparative cost of the different methods of entry, the drift
is of course the cheapest. In this method the very first blow of the
pick brings down a fragment of coal that may be sent to market and
sold. For this reason the sinking of a slope is less expensive than
tunneling or shafting, because the excavation is made in the coal. It
may be said to cost from twenty-five to fifty dollars per linear yard
to sink an ordinary double track slope, from fifty to seventy-five
dollars per linear yard to drive a tunnel of average cross-section to
accommodate two tracks, and from three hundred to five hundred dollars
per linear yard to sink a shaft with four compartments. Of course
circumstances, especially the character of strata, may greatly increase
or lessen these limits of cost. Indeed, it has happened that a shaft in
process of sinking, which had already cost many thousands of dollars,
has been necessarily abandoned because an intractable bed of quicksand
has been encountered.
The experienced coal operator, knowing the advantages and disadvantages
of each of these methods of entering a mine, and the adaptability of
each to his particular coal bed, will find no difficulty in making a
selection from them. Indeed, there may be, and usually is, practically,
no choice. The selection of a site for the opening is ordinarily
attended with but little more freedom of choice. The outcrop, if there
be one, the topography of the surface, the outline of the coal seam,
the accessibility of the spot, the location of the breaker, all govern
in the selection of the site, and usually all point to the one most
available spot.