system was adopted in a portion of the mine to get coal rapidly; for, at this point, a short-grained, slate cap rock came in over the coal, making it difficult to keep props in place. The floor is a close blue slate and has a decided heaving tendency. The roof is an excellent sandstone. There is a small but troublesome amount of gas. Two double chutes are driven up the pitch at a distance of 36 ft. apart, connected every 40 ft. by cross-cuts. One side of each chute is used for a coal chute and the other for a manway and air-course. At a distance of 12 yd. apart small gangways are driven parallel with the main mine gangways. These are continued from each chute a distance of 300 ft., if the conditions warrant it. The top line is then attacked from the back end and the coal is worked on the cleavage planes; the breast, or room, therefore consists of a 12-yd. face, including the drift or gangway through which the coal is carried to the chutes; a rib of coal (2 or 3 ft.) is left between the breasts to keep the rock from falling on the breast below. Thus in each breast the miners have a working face of about 15 or 16 yd., and as the coal is directed to the car by a light chute, moved along as the face advances, the coal is delivered into the cars at small cost, and but little loss results from the falling coal, as a minimum of handling is thus obtained. Immediately above each gangway, and starting from these main chutes, an angle chute is driven at about 45°, connecting with a part as the gangway chutes (30 ft), at an angle of 35°, and cross-cuts are driven the breast gangway above it, and into these chutes the coal from that breast

FIG. 31

is delivered, runs into the main chute, and from it is loaded into the mine cars in the main gangway. These angle chutes serve as a means of keeping the main chute full, and at the same time give each breast an opportunity to send out coal continuously. They also serve the purpose primarily intended, of saving the coal from breakage, by giving it a more gradual descent into the full chute. The breast gangways are driven 5 ft, wide. No timbers are needed in these gangways, as they are driven in the coal, except on the foot-wall or floor side, which, as before stated, is a firm sandstone. It is found safest to leave a rib of coal on the top of the breast 2 or 3 ft. thick, until the working face has passed on 12 or 15 ft., when this rib is cut out and thus all the coal extracted, the roof caving behind and filling in the opening. As cross-cuts are driven every 36 ft., ventilation is kept along the working faces, and a safe and effectual means of securing all the coal in the seam is thus attained.

Fig. 32 shows another system used in No. 7 vein at the same place. The seam averages 7 ft. of coal. The roof is shelly and breaks quickly, hence the coal must be mined rapidly.

In this system the gangway chutes are driven at right angles with the strike of the seam, 40 ft. up the pitch; a cross-cut 5 ft.X6 ft. is then driven parallel with the gangway. From this cross-cut, chutes are driven at same distance every 40 ft. between chutes, for ventilation. After a panel of five or more chutes is driven up the required distance, work is commenced on the upper

outside pillar and the pillars on that line are drawn and the next line is attacked, and this is continued until the panel or block is worked down to the crosscut over the gangway. About every 80 ft. in this level it is found advantageous

to build a row of cogs parallel with the strike of the seam as the pillars are drawn. This serves to save the crushing of the pillars, and prevents any accidents from falls of rock. But few timbers are required by this system.

PILLAR-AND-STALL SYSTEMS OF MINING

The pillar-and-stall system, also known as post-and-stall, board-and-pillar, or stoop-and-room, is a modification of the general room-and-pillar method in

which the openings, usually called stalls or rooms in America, are narrow, rarely exceeding 4 or 5 yd. in width. The pillars are at least as wide and usually wider than the stalls. In the single-stall system, the stalls are turned narrow off the entry as shown in Fig. 1 (a), and widened inside as described in room-and-pillar work. In the doublestall system, shown in (b), the openings are wider, and are similar in every respect to double rooms, except that the pillars separating the double stalls are generally wider in proportion to the width of the stalls than are the pillars separating rooms. In double-stall work, the openings are often 12 or 15 yd. in width, the roof being supported on good pack walls in the center of the stall; the pillars often reach a width of 30 yd. The pillar-and-stall system is adapted to weak roof and floor, to strong roof and soft bottom, to soft, brittle coal, and in general to conditions requiring ample support of the roof; the system is particularly useful in deep seams where the roof pressure is great.

(a)

FIG. 1

(b)

Connellsville Region.-Fig. 2 shows the common method used in the Connellsville, Pennsylvania, region. The average dip is about 5%. The face and butt headings are driven, respectively, at right angles to each other on the face and the butt of the coal. The face headings leave the main butts about 1,000 ft. apart, while from these face headings, and 400 ft. apart, secondary butts are driven, and again from these butts on the face of the coal the rooms or wide workings are excavated to a length of 300 ft., this having proved the most convenient length for economical working. Room pillars have a thickness of 30 to 40 ft., while the rooms are 12 ft. in width and are spaced 42 to 52 ft. between centers, depending on depth of strata over the coal. The headings are 8 ft. wide, and in all main butts and faces the distance between centers of parallel headings is 60 ft., leaving a solid rib of 52 ft. A solid rib of 60 ft. is also left on the side of each main heading. The average thickness

of cover at the Leith mine, which is here described and which may be considered as a type of the region, is 250 ft., the overlying measures being alternate layers of soft shale and coal for 4 ft. The bottom is an 18-in. layer of hard fireclay and slate. These floor and roof materials are soft, and are easily disintegrated by air and water. At some mines, cover will reach as much as 700 ft., and the dip of 5% (as at Leith) is much heavier at some points on eastern outcrop, and will run as high as 12%, flattening off as the synclinal line of the basin is reached, until it is almost level. In some localities, the material below coal is hard limestone, requiring blasting to remove it, and at other places the roof slates are much more solid than at Leith, and not readily disintegrated. The method of drawing ribs is one of the advantages of the system, since it is harder to do successfully in a soft coal like the Connellsville than in hard coal. The coal itself is firm. When necessary to protect the top or bottom, 4 to 6 in. of coal is left covering the soft material.

The method just given is often applied to a whole series of butts (4 or 5) at once instead of to butt by butt, as shown in Fig. 2. In this case, work is started at the upper end of the uppermost butt and progresses, as shown, but, after cutting across the butt heading from which the rooms are driven, the butt heading itself and the upper rooms from the second butt, or that just before, are likewise drawn back by continuous slices being removed from the rooms of the upper butt, and on across the next lower butt, etc., all on an angle to the butts, and so continued as the operations progress, until another butt is reached, etc., thus gradually making a longer and longer line of fracture, which is only limited by the number of butts it is desired to include at one time in the section thus mined. This works very nicely and makes long

even lines of fracture, the steps of the face of the workings (in the rib drawing) being about 30 ft. ahead of one another.

J. L. Williams Method.-The J. L. Williams method of working anthracite, Fig. 3, was applied successfully by the originator at the Richards mine, Mt. Carmel, Pennsylvania, and by it 90% of the available coal is said to have been obtained. The method is a pillar-and-stall method with the following distinguishing points: (1) Timbering the gob with props set not more than 6 ft. apart, to keep up the roof during the extraction of the pillars. (2) Making holes from the crop, for the delivery of timber into the workings. (3) Removing the pillars in shorter lifts than is possible when the roof is supported with culm pillars. (4) Keeping the gob open with timber for dumping the fallen rock, that would have to be sent to the surface if the breasts were flushed.

Both the floor and the roof of the mine were weak, so that it was not possible to make either the breasts or the pillars wide. In some cases, the floor consisted of 3 ft. of clod, and to prevent its lifting and sliding, every

alternate prop was put through the clod and its foot set in the slate beneath, while the other props were set on pieces of 2-in. plank 2 ft. in length to keep down the bottom. A small gangway X is driven to take out the chain pillar, and Y is a small gangway for taking in timber.

PANEL SYSTEM OF MINING

303

In the panel system, the coal area is first blocked out by pairs of entries driven at right angles to one another if possible. As soon as the panel has been thus blocked out, the removal of the coal within the panel is begun by driving openings a, Fig. 1, from the cross-entries. These openings are connected by a cross-heading b, a suitable pillar being left between b and the cross-entry. Rooms, or stalls c are then opened off the heading b and driven almost the full length of the panel, only leaving suitable chain pillars d for the protection of the main and cross-headings enclosing the panel. After the rooms, or stalls, have been driven their full length, the pillars separating the stalls are drawn back, allowing the roof to fall as shown. The Connellsville method described under the heading Pillar

and-Stall Systems of Mining, while closely resembling the Scotch and English pillar-and-stall method, may be considered a modification of the panel system.

When a panel is worked out, in order to close off the whole panel it is usually necessary only to put stoppings in the mouths of the openings a. A pipe is put through each stopping with a valve in the pipe on the outside of the stopping. As firedamp is often given off in the panel after it is worked out, these valves should be opened at regular intervals and the issuing air tested for firedamp with a safety lamp held a few inches from the mouth of the pipe, so that any escaping gas can mix with the fresh air. If gas is found, the valve is left open

and the gas allowed to escape and should be led into the return; it is sometimes lighted at the pipe and allowed to burn off, but this is dangerous, for the flame may travel back through the pipe and explode the gas in the panel. A second pipe on which is a pressure gauge is sometimes placed in the stopping to test the pressure of gas behind the stopping, particularly when the gob is on fire and generating gases. If there is much pressure of gas behind the stoppings, the pipe through the stoppings should be left open when the men are not in the mine. In some cases, the pipe through the stopping is connected with a pipe laid along the entries and leading into the return air-current.

The term panel system is rather loosely applied in the United States to any system of mining in which the mine is divided into a series of blocks in which blocks the pillars are drawn and that section of the mine sealed off while operations are being carried on in adjacent blocks. Thus, a tract developed by a series of parallel cross- or butt-entries, say, 350 to 500 ft. apart, is often spoken of as being worked on the panel system when the respective butt entries are not connected and the room workings from one pair of entries are not driven through to the next parallel entry, the pillars being drawn as soon as the rooms and the entries reach their limit of length, or the coal between pairs of the parallel entries may even be worked by the longwall method.

Col. Brown's Method.-Fig. 2 shows a panel system devised by Col. D. P. Brown, of Lost Creek, Pennsylvania, which gives good results in thick seams