As soon as sinking has been completed the question of laying out the workings arises. This should be done so as to comply with such conditions as may be fixed by the Mines Act, and in such manner as will best suit the method of working to be adopted.

Shaft Pillar. — The first consideration is the size of the shaft pillar or bottom stoop, which must be left in order to prevent damage to the shafts by the ground subsiding when the coal is worked away. The shape of this pillar is not important, but it is usually either roughly square or circular. Many rules are given as to its size, but the most trustworthy method of arriving at this is to take the conditions of the particular case into consideration. This is best done by keeping a record of the strata passed through and fixing the size in accordance therewith. Once the coal is removed the line of break of the strata finally creeps back to the angle of repose for that class of material. This for soil and clay may be taken as 9 feet horizontal to 6 feet vertical, whereas for average coal-measures strata it is about 1½ feet horizontal for each 6 feet vertical. If then the thickness of soil or clay near the surface, and the depth of strata passed through, be known, it is an easy matter to calculate the size of pillar that must be left to adequately protect a given area. The presence of faults within the area of the shaft pillar may necessitate some addition to its size, and where the surface consists of soft mud, moss, or running sand, it is extremely difficult to fix any definite size of pillar that will afford complete protection. In cases where the dip and rise of the seam is considerable it is necessary to leave a larger part of the pillar to the rise side of the shafts.

Position of Main Roads. — As soon as the area of the shaft pillar has been fixed the driving of the main roads is begun. These roads are laid out to suit the haulage system that it is intended to adopt in working the royalty, and are little, if anything, affected by the method of working the coal which will afterwards be followed. Generally the first 150 yards or so of these main roads going along the strike or level course will be used for sidings for loaded and empty hutches or tubs. To facilitate the movement of the loaded ones, it is desirable that these roads should rise slightly from the shaft bottom. An inclination of about 1 in 130 will be found to give the best results. These main roadways will also act as airways, and to meet the requirements of the Mines Act, where more than one hundred men are likely to be employed and where the workings are dry, three such airways must be provided, two intakes and a return. A plan showing how three such roads may be set off from both sides of two shafts, an upcast (U) and a downcast (D) is shown in Fig. 37.

Methods of Working. — Two chief methods of working are available, although there are various modifications of each. These are 'longwall' and 'pillar and stall,' or, as it is usually called in Scotland, 'stoop' and 'room.' No hard and fast rules can be laid down with regard to choice of method, but careful consideration must be given and experience brought to bear upon the question before a decision is come to. The success of a colliery undertaking is closely associated with the cost of production, and for this reason it is desirable to adopt the method that promises the most economical and safest working. Among the various circumstances that fall to be considered is the inclination of the strata, the character of the roof and floor, the depth of the seam and its character and thickness, the natural jointing or cleat of the coal, and whether the seam is close to another in process of working. In addition there may be special conditions that claim attention, such as working under the sea, working a seam known to be liable to spontaneous combustion, or working under valuable buildings, for the safety of which the colliery company may be responsible.

Longwall Working. — In longwall working the whole of the coal is removed in the first operation, the space being filled up with rubbish obtained from the roof in the roadways. As these roads run through the excavated or waste ground they decrease in size as the ground subsides. To get over the difficulty caused by the effects of the ground settling down, it is customary to cut the side roads off at regular intervals by new main roads driven through the waste. If these roads follow the direction of strike they are called 'levels,' if they run at an inclination they are called 'slopes.' The object of cutting off the side roads by means of these 'levels' or 'slopes' is to limit the total length of roadway to be kept in repair and reduce the length of haulage.

The distance between the levels or slopes varies with the conditions of the seam, and may run from 20 fathoms in some cases to 50 in others. A common distance is about 30 fathoms. The actual distance depends upon the height of the seam, size of hutch, method of haulage in side roads (horse or man), and the nature of the material available for packing.

When broken out of the roof the packing 'material occupies from two to two and a half times the bulk that it (lid in the solid. Since it can only be loosely packed in the waste ground it does not offer much support at first, but as the pressure causes the overlying strata to settle down the packing material becomes consolidated and offers a gradually increasing resistance, until, finally, it prevents further subsidence. During this consolidation soft coal measures shale (Blaes) comes down to about one-third of the original height of the packwall or building. Fakes or finely laminated sandstone comes down fully one-half, while hard sandstone comes about one-half. On an average it is found that the roadways settle down by about half the height of the seam. Thus a roadway originally 6 feet high, in a seam 4 feet thick, worked longwall, would after the lapse of a few weeks settle down some distance behind the working face to a height of from 4 feet to 3 feet 6 inches, or nearby. The actual subsidence depends not only on the class of material available for packing but upon its amount. A working where the space left by the extraction of the coal is only partly packed subsides further than a similar working where the space is completely packed. The nature of the floor or pavement, as it is often called, has also a good deal to do with the amount of subsidence. When soft the packing is squeezed down into it, and it (the floor) rises between the roadside buildings in the roadway, causing considerable trouble. The only cure for this, and at the best it may be only a partial one, is complete stowing of the waste.

In laying out a longwall section the side roads or branches may be started away from the rise side of the level, in which case they will be driven to the rise. This method of branching is best suited to a slight dip and rise. On the other hand, if the seam should lie at a steep inclination the branches are started away from the sides of the headings (main roads going to the rise) and run level course across the dip and rise, thus making the haulage of the coal much easier. Like other stratified rocks coal shows two sets of joints, the main or master set being called 'planes,' the secondary being called 'ends.' The coal is usually more easily worked if the face is advanced parallel with the plane, and in some cases the direction of the plane joints, or 'backs,' as the miner calls them, is the determining factor in fixing the direction of the branches. In cases where the coal is soft and friable the face may be advanced at right angles to the plane, and in such cases the coal is said to be worked on end. Where the joints in the coal correspond to those in the rock forming the roof, there is a tendency for the roof to become dangerous, especially if the seam is at some depth and the roof pressure great; in such cases the line of face is advanced at an angle of 45 degrees to the main joints, in which case the coal is said to be worked half-end, half-plane. The plan of a longwall section showing the branch roads and the manner in which they are cut off is given in Fig. 38.

In the actual operation of mining the coal the face is kept open by means of rows of props, or if the roof is weak props set up to bars or straps placed against the roof at right angles to the face. The side roads or branches are formed by packwalls built up on either side, the material being obtained by brushing or, as it is sometimes termed, ripping down the roof in the roadway. This provides the necessary height of side road, and supplies material to support the roof along the face of the wall. The distance between the side roads, or otherwise the length of the wall, varies from 10 to 40 yards, depending upon conditions — a common length is about 15 yards. The general appearance of a part of a longwall face showing the position of the side road and buildings is shown in Fig. 39.

Should the space between the buildings, often called the 'cundie,' be too great, then one or two intermediate buildings or pillars must be put in to steady the roof as it subsides. If this is not done then the roof may fall and come over the face timber, thus closing the place. When this takes place the coal is cut forward opposite the road, and then down the sides or wings of the place until it is past the fallen part and the face again opened.

In working the coal the miner uses his pick to undercut or hole it to a depth of from 2½ to 3 feet. As soon as a yard or so has been holed, a sprag or gib is placed under it to prevent it falling. Proceeding in this way a length of the face is holed and then the sprags are withdrawn. In some cases the coal will fall when this is done, in others it will require to be wedged down, and in certain seams where the coal is strong, or where the roof parting is bad, it may require to be blasted down. In thin seams the fallen coal is thrown back to the road to be filled into hutches, and a row of props set to support the roof at the point from which it is removed. In thicker seams it may be possible to carry a temporary track along the face, and so bring the hutch along to the place where the coal is lying. Some miners do not hole or undercut the coal to any depth beyond that which will enable them to get a little bit off the face. This is a bad way of working, as it produces more small coal, which has a lesser market value than round or lump coal, and so their labour is of less value to their employer than that of the miner who holes his place properly, and thereby secures the maximum amount of round coal.