VIRGINIA AND NORTH CAROLINA COAL-FIELDS.
the description of the Western and Eastern coal-fields, we propose now to notice briefly the Southern independent coal-fields, which exist in the primitive rocks, or on the Atlantic slopes, and are formations of a later date than the A lleghany or Western bituminous coals, which belong to the true or Carboniferous era. These are small, impure, irre gular, and insignificant deposits, compared with the great fields of the West; but being located in populous districts, remote from the regions of the true bituminous coals, they become of great local value. The cost of mining is always greater in such irregular formations, as we shall describe; but the coal is frequently pure enough for all practical purposes, except the smelting of iron, and generally of a character suitable for steam and most domestic purposes.
There are five distinct coal-formations in Virginia and the Carolinas. Three of these appear to be creations of relatively different ages, but all of later periods than those of the true formations.
The Richmond eoal-field, near Richmond, in Virginia, lies within the granite basins of the primitive formations, but is nevertheless the latest creation. The Piedmont coal-field lies farther inland, in the counties of Prince Edward and Cumberland, and is within the gneissic basins, or the crystalline, sedimentary deposits of the metamorphic era; but the coal is of an earlier period than that of Richmond. This field is, perhaps, part of or a parallel formation with the Dan River coal-field. The Deep River :oal-field, in North Carolina, is undoubtedly of a cotemporary date with he Piedmont and Dan River but the composition of its litho logical structure is materially different, owing to the character of the sources from which it was derived. The New River coal-field, in Mont gomery county, Virginia, essentially differs from all other coal formations in this country, and is perhaps the oldest coal in existence, or the creation of the proto-Carboniferous ages. The character of the strata in which it exists belongs to the Vespertine period of the Paheozoic formations, and the fossils found therein apparently belong to the earliest dates of the Carbo niferous era. Therefore, we place the New River coal-field in an older position than the great coal-fields we have been describing; while the coal fields of the East, though occupying positions on rocks of the older form ations, are still more recent in their respective creations.
The great coal-fields of the West, or, more properly speaking, of the interior portions of our continent, are among the oldest creations of coal, and the productions of the Carboniferous, or GREAT COAL ERA, when nine-tenths of the coal-deposits of the world were formed. Yet those immense deposits of coal are stratified in a comparatively late geological age, since which no great lithological structure has been created on this continent. The Permian, overlying the coal, caps the Paleozoic
column but rarely in this country, and to a very limited extent. There fore the coal measures proper may be considered the last great creation of this continent, since we consider the Lignites and Tertiary coals of the western margin of the Appalachian or ancient sea the cotemporary forma tions of those great Eastern beds of true coal. But those imperfect coals were created under less favorable conditions than the true coals of the East. The sea was shallow on its western margins, as all the circum stances—and they are numerous—prove. The vegetation may have been profuse in those shallow waters; but vegetation alone was not sufficient to form the vast coal-beds in the East, and did not form them in the West. The hydro-carbon oils, which were the productions of heat and the chemical combinations of certain minerals, as described in Chapter IV., were deficient in the western margins of the great basin, or ancient sea; and, consequently, the coal is also deficient and imperfect.
It may seem strange to those not familiar with geology and the circum stances attending the creation of coal, that the coal-fields of Virginia and North Carolina, which exist in the oldest rocks, should be of still later date than the fields reposing on our latest creations; but this apparent irregularity can be clearly explained, we think, on the principles advanced in Chapter III.
When the coal-fields of the interior—which we often speak of as the West, more from habit than from propriety—were in course of formation, the rocks in which the Southern coal-fields exist occupied an elevated posi tion as a great coast-range of granite mountains, washed on the west by the waves of the ancient Appalachian Sea, and on the east, perhaps, by the Atlantic. But the position of those Eastern coal-beds was then high above water-level and destitute of all the conditions necessary to create coal. Since the formation of the Palxozoic strata and the coal measures they sustain in the ancient sea, the great coast range subsided. Perhaps the subsidence was gradual, and, as the sedimentary strata rose, the primi tive crust was depressed, since the material which formed the one was at the expense of the other, as formerly stated in the early pages of this work.
The consequence of this change of physical structure is evident. When the granite mountains were diminished and sunk their tall heads beneath the waves of the Atlantic, and comparative quiet reigned along its volcanic shores, the small coal-fields of Virginia and North Carolina came into existence. They all ocdupy deep depressions or cavities in the primitive rocks,—perhaps the craters of extinct volcanoes,—and the materials com posing their strata or measures are the debris of the higher lands, brought down by the rivers which traverse them, and in this respect are totally unlike the coal-fields of the Carboniferous era.