SANDSTONE VEINS AND VEIN FILLING. 43 
to have been open cracks made by twisting the vein walls at the time the 
clay-vein openings appeared. 
SANDSTONE VEINS AND VEINS OF SAND 
Ina cannel mine in Beaver county, Pennsylvania, having a very strong 
roof of sandstone, probably about 120 feet thick, and where 1 foot of bitu- 
minous coal underlies the 8 or 9 feet of cannel, a nearly vertical vein of 
hard sandstone intersects the series. This vein varied from 2 to 6 inches 
in width, and in places contained considerable debris of cannel, with 
much pyrite and some limonite. Near Scott Haven, Pennsylvania, a vein 
of black sand is reported to have been struck in the Pittsburg coal bed 
many yearsago. Mr C. R. Keyes, of the Geological Survey of Iowa, has 
reported the occurrence of compact sandstone walls in the coal near Des 
Moines. 
IngEcTtTED VEIN FILLING 
Attention may be directed to a portion of a clay-vein represented in 
figure 12, where on the hanging wall of the vein is seen a streak of dark, 
hard, clayey material proceeding from the confluence of two thin strata 
of the same rock, which in the normal coal seam are separated by about 
4 inches of coal. It is evident that here we have an excellent example 
of the way in which parts of the vein walls, having become softened by 
Figure 12.—Injected Vein Pilling. Ficure 13.—Flowage of Clay-vein. 
One-fifteenth natural size. One-fiftieth natural size. 
water in the fissure, flowed together by pressure into the fissure, and as a 
result of lateral squeeze, accompanied by a vertical drag or displacement 
of the walls, finally reached the stage or condition seen. Figure 13, 
copied from a photograph in the possession of Mr Leo Gliick, formerly 
of the Geological Survey of Missouri, shows what seems to be a protuber- 
Vil—Butt. Grou. Soc. Am., Vor. 9, 1897 
