THE PRACTICAL DEVELOPMENT OF MINES, opening and practically developing mines of coal, much depends on the natural condition in which the coal exists. In some localities the coal is entirely in the moun tains and above water-level, as shown to be generally the case on the Great Kanawha River in West Virginia and many other places in our Western bituminous coal-fields ; while in others part of the coal is above and part below water-level, as in the anthra cite coal-fields of Pennsylvania, the vicinity of Pittsburg, and many other places ; and in other instances the coal is almost entirely below water-level, as in the Richmond coal-field, the English Newcastle mines, &c. &c.
Drifts, levels, or gangways, are generally employed above water-level when the seam can be approached without tunnelling through the overlying or underlying rock. When this is necessary, rock tunnels are used, as shown in figure 139, where tunnels are made use of to reach the seams, below water-level, though both underlying and overlying ; but above water-level tunnels are seldom required to penetrate the under lying strata in order to reach the seams. This condition sometimes happens, however, where the seams have a low angle of dip into a mountain-side, and cannot be followed by drift on the seam on account of water. In this case a tunnel is started below the seam and run in under it until the coal is reached.
Tunnels are galleries or subterraneous passages cut in the rock ; and " drifts," as technically called, are avenues of the same description cut through, or in, the coal. We will not, however, dwell on these, as they have been partially described in the pre ceding pages. They are the simplest modes of mining, and should always be made use of where they can be made available. As a means of draining mines they are
most effective, and may be made use of to a much greater extent than they are. For instance, a slope may be 100 yards deep and productive of a large amount of water, which requires the expenditure of $20,000 in machinery and pumps for its drainage, besides a constant expense of from 20 to 30 dollars per day in labor, oil, coal, &c., to keep in operation while the "lift" may last,—say for five years,—or a total expense of $62,000. This drainage may be effected by tunnel, in many instances, by one of from 250 to 500 yards in length, which at $40 per yard would only cost from $10,000 to $20,000. In many cases where much water exists and powerful and costly machinery is made use of to drain the mines, it would be better to drive a mile of tunnel, if available, than to erect machinery and entail the expense of constant drainage. We may instance the Wiconisco mines at Bear Ridge, the Room Run mines at Nesquehoning, and some of the Wilkesbarre mines ; since one tunnel would drain several operations.
The cost of tunnelling in the anthracite regions varies from $25 to $75 per lineal yard, when miners receive about $1.50 per day. The cost depends on the measures through which the tunnel may be driven, as shown by the table on another page. For instance, the measures between the Seven-Feet and the Mammoth are soft slate, and can be worked at a low price ; the same in the vicinity of the Primrose and the Big Tracy. But in the vicinity of the Lewis, the Holmes, and the Buck Mountain the rocks are very hard, and the cost is materially increased.