48. Map of workings in Buck Mountain bed at Wolf Collieries Co., near 49. Sketch of cross sections showing rolls in room of Wolf Collieries Co-- 87 50. Map of workings in Skidmore bed 89 51. Workings in Pittston bed under Schovils Island and the Susquehanna River at Seneca colliery, near Pittston, Pa 90 52. View showing point where 400 gallons of water a minute comes from 53. View showing water coming from fissure in coal at a rate of 100 54. Metp of Marcy bed at No. 9 colliery, Pittston, Pa 92 55. Map of part of Checker bed at No. 9 colliery, Pittston, Pa 94 56. Map of part of Pittston bed at No. 9 colliery, Pittston, Pa 94 57. Map of part of Pittston bed under built-up part of No. 9 colliery, MINING OF THIN COAL BEDS IN THE ANTHRACITE REGION OF PENNSYLVANIA By Dever C. Ashmead INTKODUCTION The anthracite mining companies in Pennsylvania are confronted with the loss of part of their market because other fuels can be produced more cheaply and are finding a readier sale to buyers eager to take advantage of lower prices. In an attempt to reduce the high cost of producing anthracite and to lower the prices they must charge to earn an equitable dividend on their investment, the operators have installed the most modern equipment for generating power, the most up-to-date haulage systems, and the best coal-preparing machinery on the market. They are also instructing the public in the use of the smaller sizes of anthracite. Nevertheless, as yet they have made relatively slight improvements in the methods of mining the coal and hauling it from the working face to the main arteries of transportation underground. In districts where the coal measures are relatively flat, operators have begun to study mining by machines and mechanical transportation from the working face to the haulage roads and are introducing these methods into their mines. One of the purposes of the work of the Bureau of Mines is the increase of efficiency in mining. This bulletin attempts to describe the progress made in mining and handling coal mechanically in the thinner' beds of the anthracite region, to point out what methods have been successful or unsuccessful, and to show the opportunity for thorough development of new mining methods. As an extended description of all the methods now in use in the anthracite region would be too lengthy for the present report, only those now employed in the thin, flat measures—that is, beds 5 feet and less in thickness and not steep enough for coal to run on—are described. ACKNOWLEDGMENTS The author acknowledges his indebtedness to those persons who have assisted him by giving information and constructive criticism. He thanks especially the coal-company officials who permitted inspection of their collieries and gave data and information; 1 R. V. Norris, for advice when the work was begun; J. W. Paul, senior mining engineer, M. van Siclen, formerly engineer in charge, research division, and J. A. Davis, mining engineer, of the Bureau of Mines; G. S. Rice, chief mining engineer of the bureau, for information on mining methods in Europe and in the bituminous-coal fields; and J. J. Walsh, secretary, and Frank Hall, assistant secretary, of the Pennsylvania State Department of Mines, for statistical data on mining methods in the anthracite region. HISTORICAL RESUME During the early days of anthracite mining the supply of coal was believed inexhaustible, and only the cream of the beds was considered minable. If the proportion of ash was slightly high the bed was considered unworkable, for no mechanical cleaning devices were used and the only method of cleaning the coal was by hand.1 Impure portions of the bed were left in place, if possible, and only the good coal taken. For example, the Mammoth bed at one place in the "Western Middle coal field was 24 feet thick and in three benches. The top and bottom benches were considered impure, and only the middle bench (8 feet thick) was mined. After first and second mining of this bench the whole bed was marked on the maps as completely worked out. In later years explorations revealed the true condition of the bed, and when the area was reopened mining was much more expensive than it would have been if the bed were virgin. Large areas were worked over by this system of mining, and the virgin coal available in the thick measures rapidly decreased. As the demand for anthracite became heavier, and unworked areas of the thick, clean beds grew smaller, it became necessary either to reopen the worked-over thick beds or to turn to the thinner beds that had hitherto been considered unworkable. Fortunately, new inventions for the preparation of coal have2 made possible the production of marketable grades of coal that otherwise would have been unmarketable. No new methods of mining had been developed, and the old system that had been used in the mining of the thicker beds for many years had to be employed in working the thinner beds. These methods were particularly inefficient and expensive in the thin beds, and the cost of producing coal from the thin beds was excessively high; indeed, in many mines it is still so. Therefore it was necessary to mine both thick and thin beds at a colliery. The thin beds were mined to allow the proper rate of production to be maintained 1 Ashmead, Dever C, "Advances In the preparation of anthracite": Trana. Am. Inst. Mln. Eng., vol. 66, 1922, pp. 422-513. and the plant to be run at its most efficient output; the thick beds were mined so that the cost could be kept down by balancing the low cost of the thick beds against the high cost of the thin beds. The increased output could be handled without increasing the overhead. DISTRIBUTION OF TEIN COAL BEDS Thin beds occur in both the flat and the steep pitching parts of the anthracite field, but this bulletin discusses the mining of the thin, flat beds only and shows the extent to which new mining methods have been developed during the past few years. The importance to the industry of the flat beds and the extent to which future production of anthracite will depend upon them will be the first points considered. Northern field.—The table following shows the thickness and acreage of the thin beds in the Northern coal field, the amount of coal originally available in them, and the extent to which these beds have been developed: Table 1.—Thickness, extent, and development of thin beds in Northern field The ratios of developed to original areas in beds thicker than 5 feet are shown in Table 2. Table 2.—Ratios of developed to original areas, beds more than 5 feet thick, Northern field If the thickness of the beds and the percentage of the total area represented by the developed area are considered, one readily sees that in the past a notable proportion of the coal produced came from the thick beds and that a considerable amount of coal remains in the thinner beds. According to estimates of the United States Coal Commission, the Northern field originally contained 5,447,thick. Only 42 per cent of the tonnage in the thin beds has been developed, whereas 66.9 per cent of . the thicker beds, which contain 71.8 per cent of the total area, has been developed, indicating that a substantial amount remains unmined in the thinner beds of the Northern field. Eastern Middle field.—Tables 3 and 4 offer correlative data on the Eastern Middle coal field. Table 3.—Thickness, extent, and development of thin beds m Eastern Middle field Table 4.—Ratios of developed to original areas, beds more than 5 feet thick, Eastern Middle field These data also show that the beds that are over 5 feet thick have been developed most extensively. The United States Coal Commission has estimated that this field originally contained 602,491,000 tons of coal, 24 per cent of this in beds less than 5 feet thick, leaving 76 per cent in the thicker beds; but of the 76 per cent 81.2 per cent has been developed, whereas of the 24 per cent only 44.8 per cent has been developed. Western Middle field.—Tables 5 and 6 give the same calculations for the Western Middle field. Table 5.—Thickness, extent, and development of thin beds in Western. Middle field |