38  W.S. GRESLEY—CLAY-VEINS INTERSECTING COAL MEASURES. 
squeezed and drawn-out condition of the rock. This figure also shows 
that faulting exists in the vein stuff (see ff’), the walls of these minia- 
ture faults being highly polished and often striated, with slickensides. 
The individual fragments in the vein material have in many places under- 
gone change in form and coloration as well as in chemical composition. 
While some portions of the vein is of a brecciated character, others 
consist of little else than hardened clay, clay and sand mixed, or even 
mostly sand, these differently composed layers or zones ranging roughly 
parallel to the vein walls. Lumps of coal in the matrix of the veins 
always possess their original cleat, even though the same is distorted. 
Coal, when forming the vein walls, 
always retains a portion of the 
clayey vein stuff when removed, the 
latter being so tightly jammed into 
the coal as to make the two ma- 
terials inseparable. Figure 4 illus- 
trates the ragged edge of the coal 
pierced by tongues of hard clay-vein 
material in characteristic manner: 
The usual color of the vein stuff is 
eray, with irregular tinges of brown, 
green, yellow, etcetera. A close in- 
spection of much of the brecciated stuff, especially when wet, presents 
quite pretty variegated aspects, such as are seen in polished marbles. 
Figure 4.—Coal pierced by Clay-vein Material. 
Natural size. 
DISTRIBUTION OF CLAY-VEINS 
The mining of coal and of fireclay underlying the coal has revealed 
the existence of clay-veins, so far as the writer has ascertained, in an area 
no less extensive than that indicated by the letters C. V. on figure 5. 
These veins are particularly numerous in the Pittsburg coal region, as 
well as in parts of the Kanawha valley in West Virginia, especially in 
contact with the “ Pittsburg” coalseam. Whether clay-veins occur where 
. there is no coal—that is, in the ‘* Barren series ” of the coal fields, as well 
as in the newer and older rocks of the region affected—are questions 
awaiting answer. In Pennsylvania they are found entirely across the 
bituminous coal field, from Elk county on the northeast to Green county 
in the southwest. The mines in Ohio reveal them, as do those in Ilinois, 
Towa, Missouri, and West Virginia. In Pennsylvania they occur in prob- 
ably all the seams of coal from the “ Washington,” near the top of the 
series, to the “Clarion,” near its base. Much of the “Sewickley” or 
‘“Redstone” bed is so much disturbed by clay-veins of one kind or 
a 
