Bulletin, 第 245 期

advancing amount anthracite region approximately areas average block boreholes bottom break breasts capacity cars cent centers chamber clay coal colliery completed connecting continue conveyor cost cross developed difficulty district driven Dunmore employed engine extends face feet thick feet wide field Figure fire floor foot four gangway gives handling hard heading hoisting inches increased laborer length less lines loaded longwall lost lower machine method Middle miner mining methods Moisture moved necessary obtained opening Operating packed permit pillars pipe pitch possible present probably production props pulled recovered recovery removed roadways rock roof rope sandstone scraper second mining shaking chute shown shows side silt slice slope space surface Table taken territory thin beds timber turned Twin upper valley