SLACK-VEINS OR SOOT-VEINS. AT 
to be foreign to the Coal Measures; in most cases the vein stuff comes 
by descent from the walls. 
“ SLACK-VEINS ” oR “Soot-VEINS” IN THE CoAL MEASURES OF WESTERN 
PENNSYLVANIA 
Of somewhat frequent occurrences in the southwestern part of the 
Pennsylvania (and perhaps in other seams as well), and brought to light 
by the mining of the Pittsburg coal seam, are reverse or overlap faults. 
These faults, while of comparatively small vertical throw, often extend 
for distances of several thousand feet across the mines. Figure 17 is a 
Figure 17.— Vertical Section in Mine at Buena Vista. 
One-sixtieth natural size. 
vertical section showing the appearance of one of those overlaps in a 
mine at Buena Vista, Pennsylvania. ‘This particular fault—a compara- 
tively simple instance—has been repeatedly driven through and the coal 
removed from both sides of it for a mile and a half in the southerly direc- 
tion in which it runs nearly straight from Buena Vista. These over- 
laps are called slack-veins or soot-veins, because the fault planes where 
they pass through the coal contain rather compact veins or seains of 
crushed and ground up coal sometimes several inches in thickness. 
The veins of soot in this instance occupy the lines or planes between 
X X’ and A B in figure 17. The walls of these slack-veins are often 
highly slickensided. These slides or overlaps extend above as well as 
below the coal bed and in many cases they seem to spread or branch out 
laterally in the overlying rocks, especially in the roof coal and shales, 
over considerable areas. Where they pass through the latter strata very 
complex contortions and inversions may generally be seen in association 
with them. In some instances a slack-vein consists of a number of short 
and irregular fractures in the coal, accompanied by a complex system of 
small overlaps crumpling and twisting the coal. That the coal and its 
accompanying layers of shale often exist under considerable strain seems 
evident from the tendency of the tops or sides of the excavations, when 
in contact with them, to suddenly break down, as if getting relief from 
or expanding under the stress. 
