THE COAL MEASURES.
That the Paleozoic strata thin or depreciate in a westward direction has been clearly demonstrated; and we may presume that the coal measures are no exception to the general rule.
But the depreciation of the coal measures bears no proportion to the depreciation of certain subordinate rocks. We have seen that the ozoic column at Pottsville is from 30,000 to 40,000 feet in height; while in the Central coal-field, in Indiana and Illinois, it is less than 3500 feet. But while the coal measures in the anthracite regions, within the pro ductive strata, are 2500 feet thick, the coal measures of the Great Alle ghany coal-field are about 2000 feet thick within the productive measures; and while the coarse sandstones accumulated in the former region, the slates, shales, €4r,c. formed in the latter; while the immense beds of anthra cite coal were forming in the East, limestones accumulated in the IreA: both required seasons of rest and quiet. Therefore, less depreciation appears in the coal measures than in the rocks on which these measures rest. In figure 117 the measures or coal-fields appear to depreciate rapidly in a westward direction, and this is really so. But this depreciation is due more to the absence or want of the measures containing the upper coals than to a thinning of the strata.
The Pittsburg coal G does not exist west of the Ohio to any great extent. It may appear on the highest points of the Illinois Central coal field, but never westward of that locality.
The natural position of the Mammoth, or E, is beneath the Mahoning sandstone, and as the Primrose, or G, is the next seam of importance above this sandstone, we must assume it to be the Pittsburg bed. The evidence of this identification is complete. First, the distance from A, or the con glomerate, in the Pottsville section, or in the anthracite regions generally, to E, or the Mammoth, is about 400 feet, and the distance from A to E in the Alleghany coal-field is generally about 300 feet. Second, the iron ore over the bed B, accompanied by limestone, is identical with the ores found over the Buck Mountain bed in the Lehigh region, at Barclay, in Bedford county, and elsewhere in the East. Third, the iron ore under bed E is
almost universal throughout the anthracite regions, and in many places in the East it is accompanied by a coarse, calcareous rock, identical with the "Curlew limestone" of the West. Fourth, we have, in our description of the principal seams in the anthracite regions, called particular attention to the "splitting" of the beds in a westward direction, and demonstrated that the Buck Mountain B and the Mammoth E each divided into several seams as they ranged westwardly; and, if we notice the sections made in various Western localities, we will find that these great beds have their representatives in their proper places and in uniform order, or are repre sented by groups occupying their proper geological horizon.
We must here call attention to a singular fact—for such we presume it to be—in regard to the cannel-coal seams. These seams have no fair repre sentatives in the anthracite regions, and are not to be identified generally in the West. They always exist between the great beds, and increase and decrease, and improve and depreciate in quality, according to the uniformity of the measures and the accompanying bituminous beds. Sometimes these cannel seams are represented by a small strata of pure bituminous coal, and at other times by a bed of bituminous shale, which changes from shale to bituminous coal, splint, and cannel, according to circumstances.
The first cannel seam exists over B, and is synonymous with our C, which is always a variable seam, and generally small. The next is a split from E, and is one of its lower benches. This seam is not reliable, and only occasionally cannel; but sometimes it is very good, and 3 feet thick on the Kanawha. The next and last cannel seam exists over the Mam moth, or E, and is sometimes from 5 to 6 feet of splendid cannel coal. It may be the "seven-feet" seam overlying the Mammoth. This is supposed to be the celebrated Peytona* cannel of Coal River, in West Virginia.