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. Also called cat.
Source: Dictionary of Mining, Mineral, and Related Terms