LONG-WALL WORKING BACK, OR WITHDRAWING.
This plan of long-wall may be used in the panel or boundary system instead of the "board and wall," the only difference being in the board being carried wide and the long way narrow, and that the air is carried across the walls instead of through divided ways. In fact, the boundary system, as set forth in the last chapter, is a compromise between the board and wall and the long-wall. Instead of carrying forward a regular chamber or breast, in which the miner can cut his daily task of coal, the long-wall miners simply carry forward narrow ways, like "headings," at great expense, and from which all the material must be removed. The withdrawing or working-back process is the same, except that the long-wall plan leaves nearly all the coal to be worked on withdrawing, while the former only works back half the coal or that left in the pillars. But either plan is far better than any now in general use among us.
The writer remembers distinctly experiments made in a thin and slaty coal-seam in the Richmond coal-field, with negro miners principally.
Three of the plans laid down in page 416 were tried, but it was found that the seam was too thin and poor to pay. The miners could not cut more than five "bogies" of 10 bushels, or 750 pounds, each, per day. But on changing the plan to long-wall work advancing, and using timber and slate to preserve the tram-ways, the production was increased to ten bogies per day, and all the coal was taken out, instead of one-third, as before.
The advantages of long-wall advancing are numerous in thin, flat seams above water level ; and no plan is better, where timber or rock from the roof can be had to keep up the roads in an available manner. But in deep mines, where the gas is abundant, long wall must be used on the "withdrawing" or working-back mode, either by going to the boundary of the estate, or by dividing the mine into panels or subordinate boun daries. We would prefer, however, to make use of the "board and wall" plan, or "breast and pillar," as shown in the boundary system; since in that the miner can produce a fair amount of coal advancing, and will have all the advantages of any other plan in withdrawing; while he has room to stow away his refuse,—slate, bone, dirt, &c.,—instead of sending every thing to the surface in advancing, as must be done by this plan in long-wall work.
We do not think it necessary further to illustrate the English board and wall system, since it cannot be comprehensively done in the small wood-cuts which we are using, and we have determined not to make use of large lithographic designs, not only on account of the time and labor necessary to produce them, but because they are inconvenient in book-form. Should it be required, the author will give personal attention to this matter, and furnish full and complete information on the subject.