LOCATION OF MINES.
In some cases there is not much choice of location; but generally there is some point more available than another in reference to the permanency of the mine and the economy of mining the coal. In this country regard is too often paid to outside or surface advantages, at the expense of general availability. But there are advantages of importance to be taken into consideration in the location of the outside establishment fl9 well as the inside workings, in regard to the cost of erecting the buildings, the loca tion of machinery, the movements of the coal from point to point, disposition of roads for the cars, room for refuse, &c. &c. But in regard to the internal working there is no remedy. When a hole is sunk in the ground, and the shaft established, there is no removing it, though it may be greatly in error, or in the wrong place. When the mine is established on the dip of a basin, the point of its location is not of so much import ance; but, even in this case, the division of the boundary, the increase and decrease of dips, and the position of "minor rolls," or subordinate basins, have much influence on the availability of the works. But when a basin or a saddle—that is, the synclinal or anticlinal axis—is to be reached, it is important that the location of the shaft be correct, or in such a position as to command the coal without the use of dip-workings. We may cite many cases where shafts have been located wrong by a few hundred feet only, yet enough out of the way to occasion great expense and niuch inconvenience and cost in mining operations.
In sinking to the bottom of a basin it is not always possible to reach its greatest longitudinal depth, as some basins are of great length ; but it is almost always possible to reach its transverse depth; and this is the most important, because the dip is always greater in this direction than in the former, as may be observed by contrasting the sections in figure 22.
The proper location of shafts, therefore, will be a question of seine importance in the future, when our deep basins must be developed; and, since they are generally irregu lar, having their axis rather to one side of than in a line with the apparent surface-axis, we have given an illustration of the proper positions, and pointed out the errors that might occur if the conditions represented are not observed.
In figure 149, we give the general form of our anthracite basins in the Pottsville district; and, while the same form does not hold good in the other districts, the prin ciple is general, though the formations are less abrupt in a northern and western direc tion. It will be observed that the bottom of the basin or the centre of the synclinal axis lies nearest to the steep side, or where the dip is greatest. This is a natural con sequence, and is invariable. The centre of the basin appears to be at the dotted line a' a', judging from surface indications, and an inexperienced person would naturally commence to sink at this point; and the error would be serious, since half the coal in the basin would lie to the dip side, and could only be obtained by dip workings or the extension of the shaft below the coals, which are then reached from the bottom of the shaft by tunnels. The process would be tedious, expensive, and inconvenient, as a
tunnel would be required for each seam.
By a little observation and calculation it may be conclusively determined that a is the proper place for the shaft, and that, by sinking here, several important advantages will be secured: the cost of sinking through and in the vicinity of a coal•bed is one-half less than that of sinking through the measures, as at a' a'; the shaft can be sunk in half the time, and the saving for a shaft 1000 feet deep would not be less than $50,000, while the coals of the basin would be reached at a point where they would all, be commanded without dip workings, &c.
It will be observed that the natural consequence of the formation represented is to throw the apparent centre of the basin far to the right of its real position, while the actual centre is as naturally thrown to the left. The same result happens to the anti clinal or saddle. Each seam has its axis progressively thrown to the left, and a shaft at the dotted line b, would strike the axis of the upper seam, but would miss the axis or saddle of the lower one considerably, and be seriously in error if it were calculated to work both basins by slopes from the bottom of the shaft. But a shaft at b, b, to the axis of the lower seam, would not only be in proper position to command the coal of that seam, but all the seams in both basins, since the slope in passing the roll c, c may be continued in its proper direction on the dotted line f, f. But the continuation of the slope through the slates would be best accomplished after the extraction of the coal from the point c' to the bottom of the shaft, or all the coal of the roll and above it, since this would form the second "lift" according to our scale, supposing the shaft a to be 1000 feet deep. We have given the shaft c, c, and the dotted line c', to show how a shaft may be sunk in error even on the dips of a basin; but the location of a shaft at this point depends on future operations. If it was designed to work the dip-coal by slope from the bottom of the shaft, then the location at c' would not be wrong, since the roll and the upper coals could be reached by tunnel ; whereas, if located at c, c, slopes would be required on the principle of f f, in order to reach the dip coal, which would be more expensive than tunnels from e to reach the upper coals. But, in case it is not intended to work the dip coals by slope from the bottom of the shaft, it is better to sink the shaft at c, c.