VERTICAL SECTION AT POTTSVILLE Figure 76 represents the coal measures in the deepest part of the anthracite fields. The section, however, only includes the productive strata, and terminates with the upper vein N, above which 500 feet of unproductive measures may exist. Measured in the centre of the deep basins, the distance to the first workable veins would be over a thousand feet; but this measurement could not be vertically across the strata, or at right angles to the veins. We think our measurements are rather tending to the mini mum than the maximum thickness, as a com parison,, with other sections would indicate.
The number Of veins shown as workable beds in our section is 15, but we have only 14 distinct names, since the "Seven-Feet," immediately overlying the Mammoth, is only a leader of that great bed, and fre quently incorporated with it. We have, therefore, not given it a location and a name, because its existence as a separate vein is un certain and temporary.
The lower vein, A, though a consistent and uniform bed, varying from 2 feet to 6 feet, is not often workable. It is more fre quently small and impure than otherwise.
C is likewise a rather uncertain seam, and is not often workable, but is always con sistent and in place, though not always de veloped or noticed.
There are nine or ten small seams, ranging from eighteen to thirty inches, not considered workable, and a number of still smaller seams, not recognized or noted in mining operations. How many of these small strata exist in the coal measures we have no means of correctly ascertaining, but presume them to be from 10 to 15, and the whole number of seams, both small and large, in the anthra cite measures, about 40. The 15 beds which we have given as workable coal have an average thickness of 123 feet in the Southern field, but the maximum thickness of the lower or white-ash series alone is often 104 feet. The unworkable seams contain about 27 feet of coal, and the total thickness of coal is not less than 150 feet.
We may now proceed to give a description of each bed as they occur in the column, remarking their identity with the same bed in other regions, as illustrated in our pre ceding sections.