COLLIERY 69 .slips and narrow dikes or walls of rock some- times occupy cracks in the coal beds, but these do not penetrate above or below the bed. The great dikes and slips found in the English and some of the French coal strata are unknown in American coal fields, which, with the exception of the anthracite fields, are singularly free from faults and dislocations. But the anthracite fields of Virginia and New England are still more seriously injured, and Fin. 10. Slip Dike. even partially destroyed, by faults resulting from excessive heat, violent lateral contrac- tion, and the consequent contortion of the strata and pulverization or partial consump- tion of the carbon. These irregularities are important considerations in the establishment of collieries, as permanence and success de- pend greatly on the uniformity of the coal bed and the purity of the coal. These and other considerations have made the anthracite busi- FIG. 11. Change of Horizon. ness more precarious and costly than the bitu- minous, and in all countries where anthracite is mined these peculiarities are observable to a greater or less extent. In addition to the cost of the great coal - preparing establish- ments, which frequently amounts to $100,000 or $150,000, the expense of sinking the pit or slope and opening the mines is also much greater than in the bituminous regions for corresponding depths. Both the measures FIG. 12." Trouble "volcanic formations. and the coal are harder in the former than in the latter ; and while the mining is conducted with but little powder in the one, the other re- quires immense quantities. Anthracite is almost exclusively obtained by blasting. At some of the mines more than 500 kegs of powder are used per month. The value of these collieries ranges from $30,000 to $500,000 each, but the average value cannot be less than $100,000 for the 437 collieries in existence in 1871, at which 52,227 men and boys were employed. The United States census of 1870 makes the value of 1,550 colliery establishments of the country $86,087,251 ; while the wages paid the 93,805 men and boys employed is given at $43,647,- 118. Hitherto the greatest amount of the Pennsylvania anthracite has been mined from the outcrops of the beds, by drifts, tunnels, and slopes ; but as this portion of the beds ap- proaches exhaustion shafts become necessary to penetrate the interior of the basins. The deepest shaft yet sunk in the anthracite fields is the Dundee pit in the Wyoming field, S. W. of Wilkesbarre, which is 7*00 ft. deep ; but it only penetrated the upper beds, when it was 3 FIG. 18. Section of Slope. a, travelling way; 6, 6, hoisting ways; c, pump way; d, pump. 1, 1, legs ; 2, centre props ; 8, coDar ; 4, sill ; 5, backing or laggins. abandoned. The next in depth is the great Hickory shaft near St. Glair, in the southern anthracite field, which is 680 ft. deep to the Mammoth bed. Near the latter two large pits are now in progress (1873), which are each ex- pected to penetrate 1,500 ft. to the same bed, and to cut nine or ten workable beds above the Mammoth. The depth of the slopes varies greatly ; some of them have penetrated 900 ft. vertically and from 1,200 to 1,500 ft. on the inclination of the bed. The large slopes are often 20 to 24 ft. wide and 7 to 10 ft. high, and provided with two hoisting ways and a double pump way, or a pump and a travelling way. The following table shows the number and condition of the anthracite collieries of Pennsylvania : DISTRICTS. No. Collieries. No. ShalU. No. Slope.. No. Drift. and Tunnels. Schuylkill 164 18 141 102 Northumberland Columbia . ... 88 8
18
7
52
4
4
4 11 Luzerne East 80 46 21 68 West Lehigh District 102 46 81 1 43 59 42 11 Total 487 91 298 290 | Some of the recent anthracite shafts are of very great size. Several near Wilkesbarre are more than 40 by 20 ft. in dimensions, but this is generally acknowledged to be an unnecessary | size in square or oblong shafts, as this_ form ! demands timber for support, and the timber | must be proportionately large and of great I length. This is an element of weakness and ! danger, and at best only of temporary utility.
