NUMEROUSNESS OF OCCURRENCE. Al 
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 givea 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 ina 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 
BT ps 
S2OGO 
Figure 8.—Displacement of Coal Bed by Clay-vein. Figure 9.—Disturbance of Coal Bed by Clay-vein. 
One-seventieth natural size. One-fortieth natural size. 
lying very flat, 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 bottom of the 
roof-coal layers. Note also the crushed, distorted, and displaced coal 
lavers on the right, intersected by vein-like forms of clay, admixtures 
