The progress that has been made in the science of mining coal within the last half century bears favorable comparison with the progress that has been made in the other industrial sciences. To-day the ripest experience and the best engineering skill in the land are brought to bear upon the problems connected with coal mining. In comparison with the marked ability employed and the marked success attained in the mining enterprises of to-day, the efforts of the early miners are almost amusing. The pick and the wedge were the chief instruments used in getting out coal. Powder was not thought to be available until John Flanigan, a miner for Abijah Smith, introduced it into the mines in 1818. It is said that when openings were first made for coal in the vicinity of Pottsville shallow shafts were sunk, and the coal was hoisted in a large vessel by means of a common windlass. As soon as the water became troublesome, which was usually as soon as the shaft had reached a depth of twenty or thirty feet, this opening was abandoned, a new shaft sunk, and the process repeated.

The mine operator of to-day, having decided upon the shaft as the best method of entry into his mine, sinks it to the bottom of the coal bed, so that its longest dimension shall be with the dip of the seam. Then from each side of the shaft, and at right angles to it, he cuts a passage out through the coal with a width of from ten to fourteen feet. These are the beginnings of the “gangways.” Then from each end of the rectangular foot of the shaft he cuts another passage, at right angles to the first one, about six or eight feet wide, and extending to a distance of from fifteen to thirty feet. These are the first “cross-headings.” At the extremities of the cross-headings passages are now driven parallel to the gangways. These last passages are called “airways.” When the gangways and airways have reached a distance of from sixty to one hundred feet from the foot of the shaft they are united by new cross-headings.

It is now apparent that two pillars of coal, each from fifteen to thirty feet wide and from sixty to one hundred feet long are left on each side of the shaft. Larger pillars than these may be left if the roof about the shaft should need more support. It is also apparent, the coal seam being inclined, that the level of one of the airways is higher than the level of the gangway, and the level of the other airway is lower.

It will be remembered that the design was to sink the shaft so that its foot should be nearly to the bottom of the synclinal valley or basin. If this has been done, then it is possible that the passage below the foot of the shaft parallel to the gangway actually runs along the synclinal axis. But if the bottom of the valley is still lower, the cross-headings will be driven farther down and a new parallel passage made, and, if necessary, still another. These openings now slope from the foot of the shaft downward, and in them is collected not only the water that may fall from the shaft, but, as the work advances, all the water that comes from all parts of the mine. This basin which is thus made to receive the mine water is called the “sump,” and from it the water is pumped up through the shaft and discharged at the surface. If the mine happens to be a very wet one it will require the constant labor of the most powerful pumping engine to keep the level of the water in the sump lower than the foot of the shaft. In some cases, in older workings, a section of the mine which has been worked out and abandoned is used for a sump, and then the water may cover an area many acres in extent. When a shaft has been newly sunk, the openings for the sump are the only ones that are made below the level of the foot of the shaft or below the level of the gangway. Henceforth all the workings will be made on the upper side of the gangway, extending up the slope of the seam, until such time as it may be deemed advisable to sink an inside slope to open a new set of workings on a lower level. The main gangway on one side of the shaft and the airway above it are now carried along simultaneously, and parallel with each other, and are united at distances of from forty to sixty feet by cross-headings. As soon as the last cross-heading is opened the one which immediately preceded it is walled up as tightly as possible. This is to insure ventilation. A current of air comes down the hoisting-way of the shaft, passes into the gangway and along it to the last cross-heading, where it crosses up into the airway and traverses the airway back to the cross-heading that was driven up from the upper end of the foot of the shaft. Passing down this cross-heading it comes to the air compartment of the shaft, and is drawn out to the surface by a powerful fan. This is the ventilating system of the mine in its simplest form. It is apparent that if any of the cross-headings nearer to the shaft than the last one should be left open, the air current would take a short course through it up to the airway, and so back to the shaft, without going to the extremity of the gangway at all. This gangway is the main artery of the mine; it is the highway by which all the empty cars go in to the working faces, and by which all the loaded cars come out to the foot of the shaft; it is the general watercourse by which the entire mine above it is drained, and by which the water is carried to the sump. In comparatively flat seams its height is the height of the slate or rock roof of the coal bed, but in steep pitching seams it is made seven or eight feet high with a roof wholly or partly of coal. In some cases the roof and sides are so firm that no timbering is required, and in other cases the timbering must be close and heavy in order to give the necessary support and security. The floor of the gangway must be given a constantly ascending grade, usually from six inches to one foot in every hundred feet, as it is driven inward. This is to facilitate drainage and the movement of loaded cars.

Where the strata are horizontal, or nearly so, as in many of the bituminous mines, the gangway may, and usually does, take a perfectly straight course. This is also true where the line of strike has but a single direction, no matter how steep the pitch of the seam may be. But both of these conditions are so rare in the anthracite regions that one seldom finds a gangway driven for any considerable distance in one direction. The surface of an inclined coal seam is not dissimilar to the surface of one side of a range of small hills. Any one who has seen a railroad track winding in and out along such a range, keeping to the surface of the ground and preserving a uniformity of grade, can understand why, for the same reasons, the gangway must often change direction in following the seam of coal. It must curve in around the valleys and hollows that indent the seam in the same manner that a surface railroad curves in around the depression where some hillside brook runs down to meet the stream, the course of which the railroad tries to follow; and it must strike out around the projections of the seam in the same way in which a surface railroad bends out around the projecting spurs of the hill range along which it runs. But the coal seam is more irregular and more uncertain in its outline than the hillside, and the curves in it are sharper and more varied. The surface railroad too may shorten its route and relieve its curves by bridging its small valleys and cutting through its narrow ridges. For the gangway this cannot be done. As a rule the coal seam must be followed, no matter where it leads. And it often leads in strange courses,—in courses that at times curve back on themselves like a horseshoe and point toward the foot of the shaft. The mining superintendent or engineer never knows in advance just what tortuous course his main artery may take. He cannot go over the ground and stake out his line as a civil engineer does for a surface railway; he must build as he advances, not knowing what the rock and coal may hide in the next foot ahead of him. He must be prepared to encounter faults, fissures, streams of water, diluvial deposits, and every other obstacle known to mining engineers.

There are several systems of laying out a mine for actual working after the gangway has been driven a sufficient distance. The one most commonly in use in the anthracite region is known as the “pillar and breast” system. In the bituminous mines it is called the “pillar and room,” and in the mines of Great Britain the “bord and pillar.” It will be borne in mind that the mine which is now being described is in the Wyoming region, where the seams are comparatively flat, the entrance usually by shaft, and the method of working is the pillar and breast system. The gangway and airway are not driven far, not more than two or three hundred feet, perhaps, before the openings are made for the larger production of coal. Beginning on the upper side of the airway, at such a distance from the shaft as will leave a reasonably large sustaining pillar, perhaps from sixty to one hundred feet, an opening is made and driven up the seam at right angles to the airway. This opening is called a “chamber” or “breast.” In the bituminous districts it is known as a “room.” The chamber is usually about twenty-four feet wide, though where the roof is exceptionally good its width may be increased to thirty-six feet. It is not often opened the full width at the airway. Instead of this a narrow passage, large enough to accommodate the mine car track, is driven up to a distance not exceeding fifteen feet, and it is from this point that the chamber is driven up at its full width. This narrow opening can be more easily closed in case it is desired to prevent the passage of air through it, and besides a greater proportion of coal is left in pillars along the airway to prevent the passage from becoming blockaded by falls. When the first chamber has been driven up a distance equal to its width, a new chamber is begun parallel to it and on the side farthest from the shaft. These two chambers are now separated by a wall of coal from fourteen to twenty feet thick. If, however, the workings are deep and there is danger from the weight of superincumbent strata, the wall should be made as thick as the chamber is wide. When the new chamber has been driven to a distance of twenty-five feet, or, if the mine is free from gas and the ventilation is good, to a distance of forty or sixty feet, the wall between the two chambers is pierced by an opening from six to ten feet wide. This is called a cross-heading or “entrance.” A partition is now built across the airway between the openings to the two chambers, and the air current is thus forced up into the last chamber, across through the entrance into the first, down it to the airway again, and so in its regular course back to the foot of the shaft. In the mean time progress has been made in the first chamber, and by the time the second chamber has been driven another distance of thirty or sixty feet, the entrance which will then be cut through the wall will find the first chamber still in advance. The inner extremity of the chamber is called the “face.” It is sometimes spoken of also as the “breast,” though this last name is properly that of the chamber as a whole. The wall of coal at the side of the chamber is called the “rib.” A third chamber is now begun and driven up parallel to the other two, then a fourth, a fifth, and so on; as many chambers, indeed, as can be laid off in this way without deviating too greatly from a right angle to the airway. But the face of the first chamber is kept in advance of the face of the second, the face of the second in advance of the face of the third, and so on, until the limit of length is reached. This limit is determined, to some extent, by the dip of the seam. In comparatively flat workings a set of chambers may be driven in to a distance of five hundred, or even six hundred feet. Where the pitch is steep, however, two hundred or three hundred feet is the greatest length at which chambers can be economically worked. The limit of length of chambers is sometimes determined also by an outcrop, an anticlinal axis, a fault, or a boundary line. The wall of coal left between any two chambers is divided by the entrances cut through it into a line of pillars nearly uniform in size. As soon as the second entrance from the airway is cut through the wall the first entrance is blocked tightly up, and as soon as the third entrance is cut through the second is closed, and so on to the extremity of the line of pillars. This is to compel the air current to pass up to the very face of the chamber before it can find a way across to the other chambers and down again into the airway. If the air of the mine is bad, or if the coal is giving off deleterious gases with rapidity, a “brattice” or rude board partition is built from the lower side of the last entrance diagonally up toward the face of the chamber to force the air to the very point where men are working before it finds its way out through an open entrance. These boards are sometimes replaced by a sheet of coarse canvas, called brattice cloth, which is lighter, more easily handled, and answers the same purpose.

From the mine car track in the gangway a branch track is built, crossing the airway and running up each chamber to its face. Up this branch track a mule draws the empty car, and when it is loaded it is let down to the gangway by the miner’s laborer. If the dip of the chamber is too steep—more than ten degrees—for a mule to draw the car up, a light car, used only in the chamber and called a “buggy,” is pushed up by hand, and when the dip is too steep for this the coal is pushed or allowed to slide down to the foot of the chamber. Chambers are often driven up obliquely in order to reduce the grade, or are curved in their course for the same reason.

When, on account of the steepness of pitch or a change in the direction of the gangway, or for any other reason, one set of parallel chambers is brought to a close, a new set is begun farther along with a different course.

The direction in which a gangway, airway, or chamber is to be driven is fixed by the mine boss. His bearings are obtained with a small miner’s compass, and he marks on the roof, near the face of the opening, a chalk line in the direction desired. The miner, sighting back on this line, is thus able to take his course and to keep his opening straight.

Sets of chambers similar to those described are driven up from the gangway along its entire length. This length may be limited by various causes. A boundary line of property, a fault, a thinning out of the coal seam, are some of them. They are usually driven, however, as far as strict principles of economy will allow. A gangway that requires no timbering and is easily kept in good working condition may be driven to a distance of three or four miles. But where these conditions are reversed, a mile may be as great a distance as coal can be hauled through with economy. Beyond that limit it will be cheaper to sink a new shaft or slope than to increase the distance for underground haulage.

As the main gangway progresses inward it may separate into two branches, each following a depression in the coal seam, and these branches may separate into others; so that there may be a number of gangways all keeping the same general level, from each of which sets of chambers are driven. When the chambers tributary to a gangway have reached their limit of length, and there is still an area of coal above them to be mined, a new gangway is opened along the faces of the chambers, or is driven just above them in the solid coal, and from this, which is called a “counter-gangway,” new sets of chambers are driven up the seam. It is often necessary to raise and lower cars passing from one gangway to the other on an inclined plane, on which the loaded cars, descending, and attached to one end of a rope, pull up the light cars, ascending and attached to the other end, the rope itself winding around a revolving drum at the head of the plane. This system can be put into use on any incline where the gradient is one in thirty, or steeper.

By this general system of gangways, counter-gangways, airways, chambers, and planes, the area of coal lying on the upper side of the main gangway and on both sides of the shaft is mined out, hauled by mules to the foot of the shaft, and raised to the surface. On long straight gangways the mule is sometimes replaced by a small mine locomotive, and in these later days the electric engine has been introduced into the mines as a hauling agent.

So far, however, in this mine which we are supposed to be working, not a tap of a drill nor a blow of a pick has been made into the coal on the lower side of the gangway save where the sump was excavated at the foot of the shaft. If this shaft has been sunk nearly to the bottom of the basin or synclinal axis, a short tunnel may be driven from the main gangway through the rock or upper bench of coal across the valley to the rise of the seam on the other side. A new gangway may here be driven right and left, and this area of coal be made tributary to the shaft already sunk. It often happens that a large body of coal lies between the main gangway and the synclinal axis, for these two lines may diverge greatly as they recede from the shaft. But chambers cannot be driven down from the main gangway owing to the difficulties of transportation and drainage. It therefore becomes necessary, in order to work this area, to sink a slope from the main gangway down to or toward the synclinal axis, and from the foot of this slope to drive a new gangway. From this new gangway chambers will be opened extending up the seam to the line of the main gangway, but not generally breaking through into it. The coal is run down to the lower level gangway, hauled to the foot of the slope, and hoisted up it to the main gangway. It is apparent, however, that the inclined plane system cannot work here; the conditions are reversed; the loaded cars are drawn up and the light ones are let down. To do this work it is necessary to bring into use a small steam stationary engine, or one working by compressed air. A common method is to locate the steam engine on the surface vertically above the head of the underground slope, and to carry power to the sheaves below by wire ropes running down through bore holes drilled for that purpose.

The system of slope mining by lifts, which is in common use in the Middle and Southern anthracite districts, has been explained in a preceding chapter. In this system the sump is always made by extending the slope a short distance below the level of the gangway. This gangway is driven from the foot of the slope to the right and left in the same manner as in the Wyoming region, except that, the seam being so greatly inclined, the gangway roof, or a part of it at least, will usually be of coal instead of slate or rock, and in very steep pitching seams the airway will be almost vertically above the gangway. The gangway is not usually so crooked as where the workings are flat, and having been started only three hundred feet down the slope from the surface, it often follows the coal to some low point on the line of outcrop, and is then known as a water level gangway, which is practically the same as a drift.

The system of opening and working breasts differs somewhat from that in use in the Northern field. Beginning at such a distance from the foot of the slope as will leave a good thick slope pillar for its protection, a narrow shute is driven up from the gangway into the coal to a distance of perhaps thirty feet, at a height of six feet, and with a width of from six to nine feet. It is then opened out to its full width as a breast and continued up the seam toward the outcrop, not often breaking through to daylight unless an airway or manway is to be made. Parallel breasts are then laid off and worked out by the usual pillar and breast system. If the dip is less than twelve or fifteen degrees, the coal may be run down from the working face in a buggy, dumped on to a platform or into the shute, and loaded thence into a mine car standing on the gangway. If the dip is more than fifteen degrees the pieces of coal will slide down the breast to the shute, though if it is under twenty-five or thirty degrees the floor of the breast should be laid with sheet iron to lessen the friction and give greater facility in movement. In a steep-pitching breast a plank partition is built across the shute just above the gangway, to hold back the coal until it is desired to load a car with it. This partition is called a “battery,” or, if there is a similar partition to hold the coal in the breast, a “check battery.” In this partition there is an opening through which the coal may be drawn when desired, and through which the men may also go to their work, though a separate manway is often provided. In these steep-pitching breasts the miner works by standing on the coal which he has already mined, and which is held back by the battery, in order to reach the uncut coal above him. There are various systems of shutes, batteries, man ways, etc., in use, but all are based on the same principles.

When the gangway of the first lift has reached its limit in both directions, and the breasts from it have been worked up to their limit, the slope is sunk to another distance of three hundred feet, and the process is repeated. From the gangway of the second lift the breasts are not extended up far enough to break through into the gangway above; a wall of coal is left between that gangway and the faces of the breasts, from fifteen to forty feet in thickness, known as the “chain-pillar.” This is for the protection of the upper gangway against falls and crushes, and is also necessary to hold back water from escaping into the lower level. These lifts will continue, at distances of about three hundred feet apart, until the synclinal valley is reached.

When the method of opening the mine by a shaft is employed in these steep-pitching seams, the shaft is sunk to the lowest level, and the successive sets of gangways and breasts are laid off as the work progresses upwards; that is, the slope method of extending the lifts downwards is simply reversed.

The method of mining by tunnel and drift, and by slope in the flat workings, is not different from the method already described for shafts. So soon as the drift, tunnel, or slope has extended far enough into the coal seam it becomes a gangway, chambers are laid off from it, and mining goes on in the familiar mode.

Various modifications of the pillar and breast system are employed in the anthracite coal mines, but no system is in use which is radically different.

In the “long wall system,” common in Great Britain, and used to some extent in the bituminous mines of Pennsylvania and the Western States, the process of cutting coal is carried on simultaneously along an extended face. The roof is allowed to fall, back of the workers, roads being preserved to the gangway, and the roof at the face is temporarily supported by an abundance of wooden props.

The descriptions of underground workings that have now been given have, of necessity, been very general in their character. It is impossible, in a limited space, to describe the various methods and modifications of methods which are in use. No two mines, even in the same district, are worked exactly alike. Sometimes they differ widely in plan and operation. That system must be employed in each one which will best meet its peculiar requirements. There is large scope here for the play of inventive genius. There is scarcely a mine of any importance in the entire coal region in which one cannot find some new contrivance, some ingenious scheme, some masterpiece of invention devised to meet some special emergency which may have arisen for the first time in the history of mining. Yet the general features of all coal mining methods must of necessity be the same in underground workings. No one reasonably familiar with them could ever mistake a map of a coal mine for a map of anything else under the sun.