Page:Encyclopædia Britannica, Ninth Edition, v. 6.djvu/78

Rh coals from the workings, as well as to a direct-acting pump ing engine, the flame and smoke being discharged by drifts into the upcast pit. For the purpose of handling large pieces of machinery and boilers, the level at the bottom is increased to a chamber 18 feet high, and roofed with rolled iron girders of a double T section. To protect the fillers working at the bottom, strong diagonal guard timbers are placed at S in order to deflect any materials falling down the shaft, and prevent them falling into the work ings. This is an unusually large example, but is taken from a pit in the highest state of development, and making a very large daily outturn. Fia. 5. Pit eye, Gambols Colliery Vertical Section. Method of The removal of the coal after the roads have been driven working may be effected in many different ways, according to the out coal. Pillar working. FIG. 6. Pit bottom arrangements, Cambois Colliery custom of the district, These may, however, all be con sidered as modifications of two systems viz., pillar work and long-wall work, In the former, which is also known as &quot;port and stall&quot; or &quot; bord and pillar&quot; in the north of England, &quot;pillar and stall&quot; in South Wales, and &quot;stoop and room &quot; in Scotland, the field is divided into strips by numerous openings driven parallel to the main rise head ings, called &quot; bords &quot; or &quot; bord gates,&quot; which are again divided by cutting through them at intervals, so as to leave a series of pillars arranged chequer-wise over the entire area. These pillars are left for the support of the roof as the workings advanc.3, so as to keep the mine open and free from waste. Fig. 1, Plate III. represents the oldest form of this class of working as practised in Scotland, from which it will be seen that if the size of the pillar is equal to tho wiilth of the stall or excavation, about f of the [MINING. whole seam will be removed, the remainder being left in the pillars. A portion of this may be got by the process known as robbing the pillars, but the coal so obtained is liable to be very much crushed from the pressure of the superincumbent strata. This crushing may take place either from above or below, producing what are known as &quot; creeps &quot; or &quot; sits.&quot; A coal seam with a soft pavement and a hard roof is the most subject to a &quot; creep.&quot; The first indication is a dull hollow sound heard when treading on the pavement or floor, probably occasioned by some of the individual layers parting from each other as shown at a fig. 7 ; FIG. 7. &quot; Creeps&quot; in Coal-Mines. the succeeding stages of creep are shown at b, c, d, f, and g, in the same figure ; the last being the final stage, when the coal begins to sustain the pressure from the overlying strata, in common with the disturbed pavement. &quot; Sits &quot; are the reverse of creeps ; in the one case the pavement is forced up, and in the other the roof is forced or falls down, for want of proper support or tenacity in itself. This accident generally arises from an improper size of pillars ; some roofs, however, are so difficult to support that sits take place where the half of the coal is left in pillars. Fig. 8 will convey a general idea of the appearance of sits, k, m, n showing different stages. FIG. 8. &quot; Sits &quot; in Mines. The modern method of pillar working is shown in Plate IV. In the Northumberland steam-coal district, where it is carried out in the most perfect manner, the boards are 5 to 6 yards in width, while the pillars are 22 yards broad and 30 yards long, which are subsequently got out on coming back. In the same figure is also shown the method of working whole coal and pillars at the same time, a barrier of two or three ranges of pillars or a rib of solid coal being left between the working in the solid and those in the pillars. The space from which the entire quantity of coal has been removed is known in different districts as the &quot;goaf,&quot; &quot;gob,&quot; or &quot; waste.&quot; Fig. 9 represents the Lancashire system of pillar- working. The area is laid out by two pairs of level drifts, parallel to each other, about 150 yards apart, which are carried to the boundary. About 100 yards back from the boundary a communication is made between these levels, from which other levels are driven forward, dividing the coal into ribs of about 25 or 30 yards wide, which are then cut back by taking off the coal in slices from the level tov ards the rise in breadths of about six yards. By this method the whole of the coal is got backwards, the main roads being kept in solid coal ; the intermediate levels not being driven till they are wanted, a greater amount cf sup-