cleat3 (klet)

[Origin obscure.] In coal mining, the principal set of cleavage-planes by which the coal is divided. Bituminous coal is more or le distinctly stratified - that is, divided by planes parallel to the bedding of the rocks above and beneath it. It is also almost always divided into thin layers by two sets of joint-planes nearly at right angles to each other and to the bedding. Of these two sets one is usually more distinct, and this is called the cleat. The surfaces exposed in mining on the line of this cleat, which are in reality joint-planes of the coal, are called faces and backs. Called in England board.