PRACTICAL MINING.
The first mode of working coal in the early days of mining, or from the first intro duction of system in under-ground mines, was by " post and stall," or " pillar and breast," as now practised in this country generally. The plan is to get as much coal as possible, leaving just sufficient pillar to support the superincumbent strata and secure the safety of the workmen.
Where pillars are left, attempts are afterwards made to work a portion of them by "robbing," as it is technically called. But this invariably produces a "creep," or " crush," destroying the remaining coal entirely, or so crushing it as to render it un profitable and dangerous to work ; while the permanent ways are generally injured more or less by the "crush," which affects a large extent of the mine.
The English miners for a long period followed the foregoing mode, and left from one third to one-half the seam wasted or lost in the mine ; but, while we are doing this still, they have for the last twenty years been perfecting a new and highly profitable system.
The late Mr. Buddle was the first to introduce the new system in the Newcastle col lieries. The plan is to remove all the coal and let the roof come down, thus relieving the pressure from the surrounding portions of the mine; but to prevent the crush from affecting other parts, the panel or barrier system was introduced.
The mine is laid out in panels, or boundaries, as described in our last chapter, and all the coal within the space removed as rapidly as possible. In England the mode adopted is known as the " board and wall," and consists in driving forward narrow "boards" or breasts to the end of the panel or boundary, leaving large pillars on each side. When the breasts, are driven to the extent designed,—to the boundary of the mine, or to the barrier dividing one boundary from another,—the miners commence simultaneously to "work back," or withdraw the pillars, on the principle of "long wall" working. By this plan all, or nearly all, the coal in the mine can be extracted; or, instead of leaving one-third as waste and lost, not over one-tenth will be left in the mine.
The difference between "board and wall" and "long-wall" is not great, but the modes in which they are applied in different parts of England are very dissimilar.
In Northumberland and Durham, or the Great Northern coal-field of England, the "board and wall" system is generally followed, as above described; but in Lancashire, Staffordshire, and other parts of England, "long-wall" is the mode adopted. While this mode is susceptible of several modifications, it is followed in only two general forms.
The most favored, but perhaps the least used, is to open the mine thoroughly before attempting to work the breasts; that is, the gangways, air-courses, and all the passages to the breasts are finished before the miners commence to work the coal, on the large scale. They then commence "working back," taking out all the coal and leaving the
roof to fall behind them, having their air-courses and gangways always open through the solid coal as they advance from the boundaries of the mine towards the shaft. This mode is cheap and effective eventually ; but the time required to open the mine, and the great outlay necessary before any return can be made, are effectual bars to its intro duction here, particularly when the "board and wall" in the boundary system is equally effective and available.
The second mode of applying long-wall is only applicable in small seams with good top slate, or one that produces enough falling material to build permanent ways through the excavated mine. The plan is to work all the coal as the miner advances, and build solid ways with rock or timber behind him through the excavated portions. When these gangways or roads are well built, the permanence of the ways is sufficient for all purposes; but the main avenues or gangways are always protected by strong pillars.
This mode of working we noticed particularly at Blossburg, Tioga county, Pennsyl vania, in the Morris seam, which is about 3 feet thick, with a fair roof. Immense props were used—not long, but thick—to protect each side of the passages. Hemlock or spruce trees, from one foot to three feet in thickness, were sawed in lengths a little less than the thickness of the seam, and placed in parallel rows on each side of the wagon or tram roads as the miner progressed; while smaller props were used along the centre of the breast to protect him from the loose slate. These were sometimes removed and used repeatedly, if convenient, and the roof allowed to fall between the roads. The air could not well be crossed, on account of the small size of the seam, and was, there fore, circulated through the mine and returned by a separate air-course not crossed by the tram-ways. The coal was mined remarkably cheap, notwithstanding the smallness of the seam and some mistakes in locating the mine, which prevented the natural drainage of the water. But this plan will not answer for deep and fiery mines, since the gases will in such cases accumulate in the goaves, or excavated portions, and always he a standing menace to the lives of the workmen. The following illustration may convey the idea of this plan of "long-wall" work, though we have given only a small portion of an extensive mine.