diagonal road. Panel breasts are used where the conditions are such as to induce a squeeze. Rooms are turned narrow off entries and are arranged in sets of 6 to 12 rooms, with a pillar 10 to 20 yd. wide between the sets of rooms. When the rooms have progressed a short distance from the entry, they are connected by cross-cuts, and the longwall face is carried forwards from this point. Packs are built and the roof allowed to settle, as in longwall. The wide pillars are taken out after the roof has settled. Tesla, Cal.-The Tesla, Cal., method is shown in Fig. 9. The coal seam averages 7 ft. of clear coal, and pitches 60°. This 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 NO2Seam. FIG. 10 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. Fig. 10 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. New Castle, Colo.-The following method is used at New Castle, Colo., for highly inclined bituminous seams. The coals mined are only fairly hard, contain considerable gas, and make much waste in mining. Fig. 11 shows the method used for extracting the Wheeler or thicker vein to its full width of 45 ft., and the E seam 18 ft. thick, excepting that left for pillars. Rooms and pillars are laid out under each other in the two seams whenever practicable. Entries are along the foot-wall; 30 ft. up the pitch is an air-course. as shown in B and C. Rooms and breasts are laid out MODIFICATIONS OF LONGWALL METHOD Fig. 12 shows a good arrangement of the main and temporary haulageways in a flat seam. The chief object in any plan of longwall workings is to have the permanent roadways the arteries of the system, providing the most direct route from all sections of the mine to the shaft. The temporary roads or working places are only maintained for a distance of 60 to 100 yd., until cut off by subroads branching at regular intervals from the main roads. The full heavy lines indicate the permanent haulageways, except only the main intake airway (12 ft. wide), running west from the downcast shaft D, and the main return air-course (12 ft. wide) leading from the face on the east side to the manway around the upcast U, which is the hoisting shaft. The full light lines indicate the diagonal subroads, driven to cut off the working places, shown by the dotted lines. The stables are located as shown in the shaft pillar, between the two shafts, where they will not contaminate the air going into the mine, but will receive air fresh from the downcast and discharge it at once into the upcast current. This position also affords ready access from either shaft in case of accident, and for the handling of feed and refuse. The pumps may be located in any convenient position at the foot of the upcast. The shaft bottoms are driven 14 ft. wide nearly through the shaft pillar, and are continued 10 ft. wide north and south through the gob. The width of all other roads and subroads is made 8 ft. METHODS OF MINING ANTHRACITE A perfectly flat seam of anthracite is seldom found in America, and even where a portion of the seam may be found lying comparatively flat, such sudden changes in dip must be expected that a system adapted to working on a pitch is almost universally used. A breast may start on a low pitch and the pitch may increase gradually until it becomes vertical, or the reverse |