A miner's term applied locally in Illinois to a bed of marcasite from 2 to 6 in (5.08 to 15.24 cm) thick that sometimes occurs between the "clod" roof of a coal seam and the more stratified shale above. The lower surface of the marcasite bed is characterized by very irregular protuberances extending downward 1 to 3 in (2.54 to 7.62 cm) into the clod.