There is only one bed of available coal on the South Side, at the base of the measures, and in basins from 700 to 1000 feet deep from the surface. The bed varies from 10 to 60 feet in thickness ; but its average size is from 20 to 30. In those deep basins the coal is very dry and gaseous, containing a large amount of gas, but producing a limited quantity of bitumen. It cokes indifferently, being too dry to form a good solid coke, but is reasonably pure. It makes an accept able gas, better than most of the Nova Scotia coals, and in larger quantities than the coals from the Eastern basins of the Alleghany field, but does not equal in quantity or purity the gas produced by the richer coals of the interior basins, or the cannels of Kanawha.
The modes of mining pursued are exceedingly primitive, and the cost of producing coal at least double that of our anthracite or Western coal fields. Experience and capital would undoubtedly remove some of the expense, and render mining more profitable ; but the formations of this coal-field are so peculiar and uncertain, that no man, however experienced in other coal-fields, should feel confident in this, without much study and investigation. With all the practical information that can be obtained, the chances will be unfavorable. It is true that most of the blunders and failures made in the Richmond coal-field are the results of ignorance,—but rather a want of local information than general mining experience. The changes are so frequent and irregular, and but seldom betrayed on the sur face, which is a series of undulating sand-hills, that no judgment, however practical, can be depended on without actual testing by proof-shafts. If a deep shaft is sunk on an anticlinal crest, where the measures are nearly flat, as is frequently the case, the work is useless ; and it is not always possible, even with the aid of exploring pits, to be certain of starting in the right locality, since those " troubles" do not always betray their exist ence in the upper strata. As we before stated, the sedimentary deposits are always thickest in the depressions, and the consequence is, that anti clinal cones of small elevation are soon covered, and the upper strata are not affected or folded by them. We do not write this to discourage the development of the Richmond coal-field, but to put capitalists on their guard. We think there are few coal-fields more inviting to the miner than the Richmond basins; but there are none where skill and engineering talents are more needed to insure success. Success, however, is certain to
those who go prudently to work and develop with sound judgment. Our sections will convey a good general idea of the formations ; but we do not pretend to show the numerous undulations or "troubles" which exist within the principal basins.
The Midlothian and Clover Hill mines are the principal works on the South Side at present, or which were in operation on that side of the James River at the commencement of the war. The celebrated Black Heath had been worked out and abandoned some years previous. The area between these points has not been proved; though coal is supposed to exist in irre gular basins almost the entire distance.
Though these mines have been worked more or less for a period of fifty years, but a small portion of the coal-field has been exhausted. Between the Midlothian mines and the James River the measures are much disturbed by the dividing anticlinal, and the change in the nature of the coal and the order of its stratification. The main bed of the south basin either splits into several smaller seams, or a new order of stratification takes place, as represented in figure 135, which is a vertical section of the measures in the basins of the north side. But the change, as before observed, takes place some two miles or more south of the river.
Through the omission of some of the figures in this section (figure 135), the thickness of the measures is not generally given. The general depth of the north-side basins is less than those of the south side, and may be estimated from 500 to 800 feet. But there are exceptions ; and we have no doubt the depth of the basin at Dover, on the west, is fully 1000 feet.
It will be observed that the order of stratification in figure 135 is quite different from that of figure 134, representing the south side, and not only the order of deposit is different, but the whole character of the formation differs. There nothing but a coarse quartzose sandstone, inter calated with slates, overlies the coal ; but here we find iron ores, trap, coke, &c.
The lower bed in figure 135 is iron ore, and lies some 50 feet above the granite, the character of the intervening space not being developed, but believed to contain only small seams of coal intermixed with slates and coarse sandstones. This bed of ore ranges from 2 to 8 feet in thickness, but is very lean, and contains but a small percentage of metal,—not over 15 or 20 per cent.