The purpose of this paper is to present a record of observations on dike-like deposits of clay and other material traversing the bituminous coal regions west of the Allegheny mountains, together with illustrations of and references to allied phenomena in other countries.
The comparative obscurity of clay-veins confines their inspection and study in situ almost entirely to such parts of them as are laid bare by such mine workings as these veins or dikes intersect or disturb. In other words, it is only a very small part, indeed, of a clay-vein that can be seen and examined, for a miner will cut or cross as few of them as possible. Nevertheless, many of them occur, and are of necessity cut and thus exposed in one place or another and at one horizon or another in the Coal Measures.
A clay-vein (also termed “clay-seams,” “ mud-seams,” . . .