Data obtained by field work and from engineers and operators, have revealed some important facts about jointing in the coal beds of Ohio. The joints show remarkable uniformity in trend, and the direction of the cleat joints appears to be the same even though more than one bed of coal is involved. In the northern part of the coal mining area, the joints occur usually in two sets known as the face and the butt joints which lie at right angles to each other. One set extends in a northeast-southwest direction and the other has a northwest-southeast trend. Farther south, one set extends in a direction a few degrees west of north and the other set, at right angles, has a trend a few degrees north of east, or nearly east and west. The joints are arranged in an arc, the convex side to the west. This curve corresponds to the curve in the folded Appalachians in central and eastern Pennsylvania, in the same latitude.There is varied opinion as to the origin of the cleat in coal, but it is difficult to explain the remarkable uniformity in direction of the joints, the fact that in successive coal beds in the same area the cleat joints have approximately the same trend, and the parallelism with the folded Appalachians to the east in the same latitude, unless one believes in the theory of tectonic origin. The joints were probably formed by deformation at the time the folded Appalachians were formed, although one must admit that shrinkage has taken place to some extent and that this fact cannot be denied.

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