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size to support the weight of the overburden. At the same time, <br /> the entry centers or the distance between center lines of adjacent <br /> entries should be as short as possible in order to minimize <br /> crosscut work and provide a greater percentage of the mining time <br /> for advancement in the field . Entries and crosscuts are mined on <br /> 60 to 100 foot centers, 20 feet wide, with a height equal to the <br /> seam thickness up to a maximum of 12 feet . The pillars that <br /> remain are recovered later to the extent that safety considerations <br /> permit . <br /> The continuous miner cuts the coal from the <br /> face and loads it into shuttle cars . The shuttle cars haul the <br /> coal to the dumping point and dump it into the feederbreaker. <br /> Here the coal is broken to an 8-inch size and fed onto a conveyor <br /> belt and transported outside to the surface coal handling facilities . <br /> (3) Longwall mining <br /> Mid-Continent believes that longwall mining <br /> is the best and safest means for achieving a high resource recovery <br /> from steep seams situated under heavy cover . Consequently, this <br /> method (either advancing or retreating) is being used where the <br /> cover exceeds 2000 feet . An added advantage of the longwall <br /> method is that methane gas emissions are less sporadic since the <br /> slow rate of face advance allows sufficient time for the methane <br /> to "bleed" into the ventilating current . <br /> The longwall method mines a solid block of <br /> coal 600 to 900 feet wide and 2, 000 to 6, 000 feet long . Coal is <br /> cut along the entire width of the face by a shearer . The coal <br /> falls into an armored chain conveyor that takes the coal to the <br />