Page:The American Cyclopædia (1879) Volume V.djvu/71

COLLIERY one direction, or that may be nearly horizon- tal. These elevations and depressions thus formed in the coal beds are locally termed saddles, horsebacks, swells, troubles, &c. ; Fia. 5. Alleghany Coal Measures. a, location of drift; /, improper location; &, location of slope ; &', location of tunnel ; c, location of pit. where they are frequent they interfere seri- ously with the drainage. In locating col- lieries these peculiarities of dip are important questions, which may generally be determined by surface indications, when the coal beds and accompanying strata are above the water level. Yet hundreds of thousands of dollars are fre- quently expended in building railroads, houses, and other colliery appurtenances, before these preliminary investigations are made, and when it is too late to remedy the great inconve- niences entailed. Many instances of this kind might be -cited in the Alleghany coal field and elsewhere. One on the Philadelphia and Erie railroad involved $500,000 of useless expendi- ture. The drift should always be located at the lowest available point of dip (&, fig. 5); but if the lowest point to which mining opera- tions should extend cannot be reached by drift, started on the outcrop of the bed and continued horizontally in the same, a tunnel may be made use of commencing in the rocky strata above or below the coal bed, in order to reach the bed horizontally, and secure natural drainage. When this mode is not available, the slope or the shaft method is resorted to. In many parts of the Alleghany coal field and its outlying basins the most productive beds of coal are on or near the tops of mountains, or at a considerable elevation above the val- leys. In these situations locomotive railroads are impracticable, and inclined planes are used ; they are operated by gravity, the load- ed cars in descending drawing up the empty cars. On the Youghiogeny, Pa., and in the Frostburg, Md., mining districts, this form of colliery establishment is in general use ; 1,000 FIG. 6. Incline and Drifts. tons of coal per day are sometimes run over a single double-track plane. The most eleva- ted coal of the Alleghany field is about 2,300 ft. above tide, while the lowest is probably 2,000 ft. below the Ohio river, near the mouth of the Great Kanawha, which is considerably deeper than the lowest coals of the central coal field in Indiana, Illinois, or Kentucky, but much less than the deepest coals of the west- ern coal field in Kansas and Colorado, where the lower coal measures are probably 5,000 ft. beneath the tertiary rocks. In the Pennsylva- nia anthracite fields, however, we find still greater diversity of mining operations as the necessary results of a contorted or highly pli- cated form of stratification, in which the undu- lations of dip are most extreme and irregular. In these anthracite coal basins every known plan of drift, tunnel, slope, and shaft is em- ployed. When the coal beds exist in the hills above the water level, drifts and counter- drifts, or upper levels, are used where the out- crop of the bed is exposed in an available lo- cality ; otherwise tunnels are made at the low- est practicable point. In these basins the coal beds usually incline at high angles of dip. However high the mountain may be on which they crop out, it is rare that they do not dip below the water level or into the basins at the base of the mountain; and still more seldom are the beds found in horizontal strata, except in the synclinals or at the bottom of the basins, where they often occur in horizontal position before curving to the opposite dip. The great basins of the anthracite fields are generally bordered by parallel mountain ranges, against the sides of which the coal beds crop out. These mountains, particularly in the interior of the fields, are cut through by numerous watercourses, which form gaps or gorges at right angles to the strike of the strata, and in these the outcrops of the coal beds descend to the water level. Thus the broken ends of the strata are exposed, and in these most of the drift collieries of the anthracite basins have been located. But when the outcrops are not thus exposed, and the elevation of the outcrop is sufficiently high above water level, the coal beds are cut by tunnels which penetrate the base of the mountains at right angles to the strike of the strata. When the coal is thus exhausted above the natural drainage, or when the amount of available coal above water level will not justify the expense of a tunnel, the slope method is generally adopted, particularly where the angle of dip is great. The slope is always formed in the coal, except when the undulations of dip require it to pass a short distance in the overlying or underlying strata. In this respect, technically speaking, the slope differs from the oblique or underlying shaft, which penetrates the rocky strata to reach the coal ; though generally a shaft is perpendicu- lar, however the strata may dip. In addition to these peculiarities of the Pennsylvania an- thracite formations and the consequent form of the mines and methods of development, a singular feature of the colliery establishments is the immense and costly structures known as breakers. These are generally masses of