Wherever possible the headings and airways were driven gob width, and the rock that was taken down to permit passage of cars and locomotives was gobbed in the space provided. However, the condition of the roof occasionally made inadvisable the driving of these headings to maximum width, and then it was necessary to transport to the surface the rock brushed from the top.

Mining has been only partly completed in the underlying beds of coal—that is, the No. 2 and No. 3 Dunmore—but wherever second mining has been completed in these two beds the room center in No. 1 Dunmore is 140 feet, with rooms 100 feet wide and a 40-foot pillar between. Where use of the 100-foot rooms is possible there are three roadways in each room—one along each rib and one in the center. These roadways are 10 feet wide, and the roof is brushed to permit mine cars to enter. When the room necks are driven, the rock that is taken down in brushing the roof must be sent to the surface; but when these necks have been driven in approximately 30 feet the three necks are connected by mining the coal in the bed, and the rock removed from the roadway is stowed in the space from which the coal has been taken. This rock is hand packed so that it directly supports the roof, and a rock-packed pillar is substituted for a coal pillar between the roadways.

Operating data.—A low-vein, shortwall mining machine is used to undercut the coal, and in rooms as previously described a machine has a 100-foot cutting face. The machine itself is 17 inches high and has been worked in places where the bed was as low as 17Vk inches. Figure 20 shows the machine working in a space only 19 inches high.

In other sections of the bed, where second mining has not been completed in the underlying beds, the rooms are driven 60 feet wide and with a 30-foot pillar on 90-foot centers. In the 60-foot rooms only two roadways are used, one along each rib, and the method of opening and driving these rooms is exactly the same as that for the 100-foot room.

Usually there is one miner to each roadway in a room, although the company prefers to have a miner and a laborer for each place.

When rooms are being driven the roadways are along the rib, therefore the rib is kept clear of all gob. When the rooms in a certain section have all been driven to their proper length, second mining will begin and the pillars between the rooms will be mined retreating. Whether it will be necessary or advisable to cut the coal with a mining machine when the pillars are being removed had not been determined when this bulletin was written.

After the coal has been undercut with the mining machine the the coal when shot tends to be thrown toward room roadways, thus lessening to some extent the amount of coal that a miner has to handle in these very thin beds. A permissible explosive is used to shoot the coal, and in a 60-foot room six to eight holes are necessary to loosen the coal. Ordinarily one 25-pound box of explosives lasts one miner two weeks.

One machine can easily undercut two 60-foot places, and some machine runners average as high as 200 feet of face cutting a day when they do not have to move too far between cuts.

In driving the headings the rock is gobbed on the chain-pillar side of the gangway, and the crosscuts are driven to the full height of the roadway.

The mine cars in the colliery have the following inside dimensions: Depth, 1 foot 6 inches; width, 4 feet iy2 inches; and length, 9 feet 5 inches. Their capacity is therefore 63 cubic feet. Their over-all length is 11 feet. Three 8-ton cable-and-reel electric locomotives are used to handle the coal from this bed. In 1925 the company had five mining machines, four of which were worked and one was held in reserve. Two more machines of the same type had been ordered.

During November, 1923, there were 50 working places and one man to a place. The 50 men employed mined 4,716 tons of coal in 24 working-days, a daily rate of 3.9 tons of coal per miner. The company has approximately the following employees in this district, exclusive of company men used from time to time: 1 assistant foreman, 50 miners, 4 machine runners, 4 machine helpers, 3 motormen, 3 brakemen, and 2 trackmen, a total of 67. This system of mining has allowed coal to be produced at a profit.

SEIULONGWALL MINING OF A THIN BED, WITH UNDERCUTTERS AND CONVEYORS AT THE PACE

One problem in the mining of thin coal beds is that of haulage from the face to the gangway. Brushing the roof to allow a mine car to enter the working place is expensive, therefore it is very desirable to move the coal from the face without having to resort to brushing. For a number of years at various places in the anthracite region drag scrapers have been employed to remove the coal from the room or from the face of the longwall. A few other methods of handling coal in working places have already been described; the use of traveling conveyors is still another method.

Bed mined.—A conveyor system has been in service for a number of years at the Dodge mine of the Baker colliery, Glen Alden Coal Co., Scranton, Pa. At this colliery the Orchard bed is 16 to 34 inches thick, it generally is flat, and the cover over the bed is 80 to 150

the coal when shot tends to be thrown toward room roadways, thus lessening to some extent the amount of coal that a miner has to handle in these very thin beds. A permissible explosive is used to shoot the coal, and in a 60-foot room six to eight holes are necessary to loosen the coal. Ordinarily one 25-pound box of explosives lasts one miner two weeks.

One machine can easily undercut two 60-foot places, and some machine runners average as high as 200 feet of face cutting a day when they do not have to move too far between cuts.

In driving the headings the rock is gobbed on the chain-pillar side of the gangway, and the crosscuts are driven to the full height of the roadway.

The mine cars in the colliery have the following inside dimensions: Depth, 1 foot 6 inches; width, 4 feet 4^ inches; and length, 9 feet 5 inches. Their capacity is therefore 63 cubic feet. Their over-all length is 11 feet. Three 8-ton cable-and-reel electric locomotives are used to handle the coal from this bed. In 1925 the company had five mining machines, four of which were worked and one was held in reserve. Two more machines of the same type had been ordered.

During November, 1923, there were 50 working places and one man to a place. The 50 men employed mined 4,716 tons of coal in 24 working-days, a daily rate of 3.9 tons of coal per miner. The company has approximately the following employees in this district, exclusive of company men used from time to time: 1 assistant foreman, 50 miners, 4 machine runners, 4 machine helpers, 3 motormen, 3 brakemen, and 2 trackmen, a total of 67. This system of mining has allowed coal to be produced at a profit.

SEMTLONGWALL MINING OP A THIN BED, WITH UHDEECUTTEBS AND CONVEYORS AT THE FACE

One problem in the mining of thin coal beds is that of haulage from the face to the gangway. Brushing the roof to allow a mine car to enter the working place is expensive, therefore it is very desirable to move the coal from the face without having to resort to brushing. For a number of years at various places in the anthracite region drag scrapers have been employed to remove the coal from the room or from the face of the longwall. A few other methods of handling coal in working places have already been described; the use of traveling conveyors is still another method.

Bed mined.—A conveyor system has been in service for a number of years at the Dodge mine of the Baker colliery, Glen Alden Coal Co., Scranton, Pa. At this colliery the Orchard bed is 16 to 34 inches thick, it generally is flat, and the cover over the bed is 80 to 150