Bulletin . the area above them. Theamount of timber used is less than one-third of that required in the cogging system. Two miners can load 75 to 125 cars daily from apillar. Powder is used only for starting a block at the batteries. WESTERN WASHINGTON. 55 LONGWALL METHOD. In the Miller bed at the Carbonado mine, where the character ofthe roof made the cost of mining by chute or breast methods pro-hibitive, a longwall system has been used. (See Figs. 24 and 25.)The bed averages 4 feet 5 inches in thickness between walls, has animmediate roof of carbonaceous shale and bone 4 feet thick, and ama
Bulletin . the area above them. Theamount of timber used is less than one-third of that required in the cogging system. Two miners can load 75 to 125 cars daily from apillar. Powder is used only for starting a block at the batteries. WESTERN WASHINGTON. 55 LONGWALL METHOD. In the Miller bed at the Carbonado mine, where the character ofthe roof made the cost of mining by chute or breast methods pro-hibitive, a longwall system has been used. (See Figs. 24 and 25.)The bed averages 4 feet 5 inches in thickness between walls, has animmediate roof of carbonaceous shale and bone 4 feet thick, and amain roof of brittle shale for at least 4 feet above the first dip is 25 to 35° in this part of the mine. A rock gangway is driven at a stratigraphic distance of 20 feetbelow the bed, and at intervals of 32 feet rock chutes are driven to 3rd level? ivrrt rrrr/r* rrmrfTTSTyTfrr. Uii/4*! (•?{?••>- ••?i>~ rrTT TTTI IT I IC- ! i ii ^+-H-J rUttW y **! r. i i i 32. Rock gangway Figure 24.—Opening out a longwall face in a coal bed dipping 35°. the coal with 10-foot chutes driven up the pitch from the ends of therock chutes, the latter being widened to form triangular connectionswith the working face. When a longwall face is to be opened, apair of chutes 10 feet wide and 12 feet apart, with crosscuts every60 feet, are first started on the full pitch of the bed. One of theseconnects with the rock crosscut leading to the rock gangway of thelevel above. When the chute from which the longwall face is to be started hasbeen driven the length of one block, a face is started from its side,as for instance at la. When the miner working this chute has pro- 56 COAL-MINING PROBLEMS IN THE STATE OF WASHINGTON. Jrdjere/^ Z?f?och gangway^Rock crosscuts ceeded the length of another step, another longwall face is startedas at lb, and at the same time the man on the lower face begins workon skip 2a, and so on. The longwall face is shown in solid lines inFigu
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectminesandmineralresou
