When necessary to protect the top or bottom, 4 to 6 in. of coal are 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 each butt in turn. 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 were driven, the butt heading itself and the upper rooms from the second butt, or that just before, are drawn back by removing continuous slices from the rooms of the upper butt, and on across the next lower butt, etc., all on an angle to the butts, until another butt is reached, etc. This gradually makes a 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.

Pittsburg Region.-The coal is worked in much the same way as in the Connellsville region, except that a different system of drawing ribs is used. The coal is worked on the room-andpillar system, with double entries, with cut-troughs between for air, and on face and butt. Entries are about 9 ft. wide, and the rooms 21 ft. wide and about 250 ft. long; narrow (or neck) part of room, 21 ft. long by 9 ft. wide. Room pillars are 15 to 20 ft. wide, depending on depth of strata over the coal, which is from a few feet to several hundred feet. The mining is done largely by machines of various types. Coal is hard, of course, and, in many places, the roof immediately over the coal is also quite hard. There are about 4 ft. of alternate layers of hard slate and coal above the coal seam. Rooms are mined from lower end of butt as fast as butt is driven, the ribs being drawn as mining progresses. As the coal is harder than in the Connellsville region, thickness of coal pillar between parallel entries is somewhat less.

Clearfield Region.-The butt and face are not strongly marked in the B or Miller seam, the one chiefly worked in the Clearfield region. Where possible, these cleavages are followed in laying out the workings, but the rule is to drive to the greatest rise or dip and run headings at right angles to the right and left, regardless of anything else. The main dip or rise heading is usually driven straight, and is raised out of swamps or cut down through rolls-very common here-unless they

are too pronounced, when the heading is curved around them. The same is true of room headings, except that they are more usually crooked, not being graded except over very minor disturbances.

Reynoldsville Region.-The average thickness of the principal seam is 6 ft. and the pitch is 3° to 4°. The coal is hard and firm, and contains no gas; the cover is light, and on the top of the coal there are 3 or 4 ft. of bony coal; the bottom is fireclay. Drift openings and the double-entry system are used. Both main and cross entries are 10 ft. wide, with a 24-ft. pillar between. The cross-entries are 600 ft. apart, and a 24 ft. chain pillar is left along the main headings. The rooms are about 24 ft. wide and open inbye, the necks being 9 ft. wide and 18 ft. long. The pillars are from 18 to 30 ft. thick.

West Virginia. In the northern part of West Virginia, the coal measures vary from 7 to 8 ft. in thickness, and have a covering varying from 50 to 500 ft. The coal does not dip at any place over 5%. In most places the coal is practically level, or has just sufficient dip to afford drainage. The usual method of exploitation is to advance two parallel headings, 30 ft. apart, on the face of the coal. At intervals of 500 to 600 ft., crossheadings are turned to right and left, and from these headings rooms are turned off. These cross-headings are driven in pairs about 20 or 30 ft. apart. Between the main headings and the first room is left a block of coal about 100 ft., and on the crossheadings there is often left a barrier pillar of 100 ft. after every tenth room.

The headings are driven from 8 to 12 ft. wide, and the rooms are made 24 ft. wide and 250 to 300 ft. long. A pillar is left between the rooms about 15 to 20 ft. wide. These pillars are withdrawn as soon as the panel of rooms has been finished. The rooms are driven in from the entry about 10 ft. wide for a distance of 20 ft., and then the width is increased on one side. The track usually follows near the rib of the room. Cross-cuts on the main and cross headings are made every 75 to 100 ft., and in rooms about every 100 ft. for ventilation.

The double heading system of mining and ventilation is in vogue.

Overcasts are largely used, but a great many doors are

used in some of the mines. Rooms are worked in both directions, when the grades are slight, but when the coal dips over 1%, the rooms are driven in one direction only; in this case, they are made as much as 350 ft. long. It is the custom then to break about every third room into the cross-heading above. The floor of this bed of coal, being composed of shale and fireclay, often heaves, especially when it is made wet.

Some

trouble is at times experienced by having the floor heave by reason of the pillars being too small for the weight they support. Alabama Methods.-Fig. 6 shows the common methods used in working the Alabama coals. The seams now working vary from 2 to 6 ft. thick, and they pitch from 2° to 40°. Where the seams are thin, the coal is hard, and pillars of about 20 to 30 ft. are used to support the roof. The rooms are worked across the pitch on an angle of about 5° on the rail, Fig. 6, A, when the

coal does not pitch greater than 20°; where the pitch is greater, chutes are worked and the rooms are driven straight up the pitch, as in Fig. 6, B. In a few cases, where the pitch is not greater than 15°, double rooms are worked with two roadways in each room, as in Fig. 6, C.

George's Creek District, Md.-Fig. 7 shows the method used in the George's Creek field, Md. The coal shows no indication of cleats, and the butts and headings can be driven in any direction. The main heading is driven to secure a light grade for hauling toward the mouth. Cross-headings making an angle of 35° to 40° are usually driven directly to the rise, and of dimensions shown.

Indiana Coal Mining.-Fig. 8 shows the method as used in Indiana. The entries are generally 6 ft. high, 8 ft. broad, the minimum height required by law being 4 ft. 6 in. The rooms are from 21 to 40 ft. in width. The mines are generally shallow. The rooms in Fig. 8 are shown as widened on both ribs, but a more usual method in this locality is to widen the room on the inbye rib, leaving one straight rib for the protection of the road in the room.

Iowa Coal Mining.-The entry pillars along the main roads are 6 to 8 yd. thick, for the cross entries 5 to 6 yd., and for the rooms 3 to 5 yd. Room pillars are drawn in when approaching a cross-cut. Both room-and-pillar and longwall methods are in use, with modifications of each. In the room-and-pillar method, the double-entry system is almost invariably used in

the larger mines. Rooms are driven off each entry of each pair of cross-entries at distances of 30 to 40 ft., center to center. The rooms are 8 to 10 yd. in width, and pillars 3 to 4 yd. The rooms are narrow for a distance of 3 yd., and then widened inbye at an angle of 45° to their full width. They vary from 50 to 100 yd. in length, and the road is carried along the straight rib. When double rooms are driven, the mouths of the rooms are 40 to 50 ft. apart, and they are driven narrow from the entry a distance of 4 or 5 yd. A cross-cut is then made connecting them, and a breast 16 yd. wide is driven up 50 to 60 yd.

The

pillar between each pair of rooms is 12 to 15 yd. In some cases, the stalls are usually turned off narrow and widened inside, the pillar varying from 5 to 8 yd. The stalls are 30 to 40 yd. in length, and the pillars are drawn back. When the stalls are driven in pairs, the pillar 8 to 10 yd. in width is carried between them.

When the longwall system is used, the main haulage road runs in each direction from the foot of the shaft, and on both sides of this diagonal roads are turned at an angle of 45°, or parallel to the main haulageway. These are spaced 10 yd. apart and driven 50 to 60 yd., when they are cut off by another