. Bulletin of the Geological Society of America. Geology. NUMEROUSNESS OP OCCURRENCE. 41 zontal distance of 35 feet, whose aggregate width was about 42 inches. The masses of coal separated by these veins were more than usually tilted and twisted. Figures 6 and 7 give a good idea of the distance which may be driven or worked over in the Pittsburg seam without striking a clay-vein, or how many are likely to be encountered in a given area where they are plentiful. Mr Albert M. Campbell informed the writer that in the Kanawha region in West Virginia, where the Pittsburg seam, usually 6 feet thick,
. Bulletin of the Geological Society of America. Geology. NUMEROUSNESS OP OCCURRENCE. 41 zontal distance of 35 feet, whose aggregate width was about 42 inches. The masses of coal separated by these veins were more than usually tilted and twisted. Figures 6 and 7 give a good idea of the distance which may be driven or worked over in the Pittsburg seam without striking a clay-vein, or how many are likely to be encountered in a given area where they are plentiful. Mr Albert M. Campbell informed the writer that in the Kanawha region in West Virginia, where the Pittsburg seam, usually 6 feet thick, thins down to about half that height over detached areas of comparatively small extent, the latter contain numerous small clay- veins, while the higher coal between them is usually traversed by one or more extra thick clay-veins. In one mine he says, " We worked out 56 acres of coal clean by supporting the mountain on the clay-vein," because of their multiplicity. As yet we have no evidence that one clay-vein intersects another clay-vein, thus showing that one was formed before the other. Faulting of Clay-veins and its Effects on the Vein Walls As shown in figure 8, the coal seam is unusually disturbed by a clay- vein, the vertical displacement being about 6 feet. Here the vein is. B ,' â â #>"C^ r^^^ ^T_ F^^, Mm /v^Wâ â¢-' - Figure 8.âDisplacement of Coal Bed by Clay-vein. One-seventieth natural size. Figure 9.âDisturbance of Coal'Bed by Clay-vein. One-fortieth natural size. lying very fiat, or rather seems to be passing from that position to a more vertical one, as traced upward through the roof coals. The clay-vein illustrated in figure 9 exhibits a very different feature. In this case we have the coal bed merely torn through and the rent filled with clayey material, while the displacement, measuring about 3 feet, is lateral and belongs to the clay-vein, which here undergoes a sudden hitch or throw, the line of fracture occurring along the bott
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