OCCURRENCE OF COAL WITH UNUSUAL CONDITIONS 321 
For a distance of 120 yards, where the sandstones are persist- 
ently inclined to the north-northeast, the tongues which split off 
from the upper part of any one coal pocket toward the source of 
the material (that is toward the southwest) rise on the surfaces of 
the inclined bedding planes. ‘This relation is best understood by 
reference to the accompanying sketches. It is this condition 
which, in part, makes uncertain the figures given above as to the 
relative thicknesses of coal and sandstone which accumulated 
simultaneously. The thickness of sandstone, except in No. 4, was 
obtained over the sandstone ‘‘trough” adjacent to the coal and 
represents the maximum over that trough, perhaps ro or 15 feet 
from the coal. This is about as far as the thin coal streaks can be 
distinctly and readily traced (except in No. 5, where they are still 
present at the point where measured); but the bedding planes, 
which are continuations of these streaks, can be followed up the 
inclinations to the southwest until they are 15 feet or even 20 feet 
above the base of the sandstone. While in the outcrop there may 
be no reason to suspect a continuation of the coaly matter upward 
along the bedding plane, slight bruising of the stone with the 
hammer edge not infrequently yields a black stain, even when the 
beds appear to be in contact with each other. This thin film of 
carbonaceous material, rising many feet along the bedding planes, 
beyond the coal laminae, makes it difficult to determine just what 
thickness of sandstone is to be considered as formed simultaneously 
with the adjacent column of coal. The thickness given in all but © 
No. 4 is that of the sandstones, which are somewhat irregularly 
bedded and lensed as a result of the thin streaks of coal and their 
compression, but measured as nearly as possible where there is no 
appreciable thickness of coal in the measurement. If measured 
farther away from the coal pocket, the thickness would be increas- 
ingly greater, but the sandstones, although carrying traces of car- 
bonaceous matter on the bedding planes, would be regularly 
inclined and undisturbed by the compression, because the coaly 
matter was too thin to cause any appreciable readjustment in them. 
Furthermore, the thickness, when measured at the point usually 
selected, agrees fairly well with the heights of the shale crests above 
the base of the sandstone troughs; these are believed to be a rough 
