42 W.S. GRESLEY—CLAY-VEINS INTERSECTING COAL MEASURES. 
of pyrites, etcetera. The maximum vertical displacement of the Pitts- 
burg seam, or any other at or by a clay-vein, known to the writer, is 12 
feet. 
Such faults as these are very variable in horizontal extent, for they 
often die out in a very few yards or may be reversed in direction of 
throw in like distances, due to reversal of dip of vein, 
“ Horses” IN THE VEIN Marertan 
In many of the larger veins in the Pittsburg coal field fallen and tilted 
angular blocks of coal or of shale and coal mixed occur firmly embedded 
in the more clayey and fragmentary vein filling. One 
<Q of these is shown in figure 1, page37,othersand smaller 
ones in figure 8, while figure 10 shows a very oddly 
twisted lump of coal, seen in contact with the foot- 
wall in the Pacific mine near Scott Hayen, Pennsyl- 
vania. That some of these “ horses” of coal may have 
belonged to the seams of coal opposite to which they 
Pee tk attra Yem- occur in the clay-veins is likely, while others have 
One-forty-fifth natural Probably dropped from seams higher in the series 
Sa when the vein was open and in process of filling. 
These “horses” of coal invariably possess the characteristic cleat. 
“SPARS ” 
Clay-veins less than 4 inches wide are called “spars.” Figures 9 and 
11 convey some idea of their forms and connection with clay-veins, the 
former being a vertical section, the 
latter (about 3 miles from the vein 
represented in figure 9) showing in 
plan six spars proceeding from one 
side of a clay-vein. On the oppo- 
site side of that vein no such pro- 
cesses were found. These narrow 
veins often injure the coal, and are 
more troublesome to the miner than 
the wider and more regular veins, 
but owing to their greater obscurity Freure 11.—* Spars” in Coal. 
and irregularity but little attention One-two hundred and fiftieth natural size. 
is paid them by the mine surveyor. 
The spars that connect directly with a clay-vein, as in figure 11, appear 
