RECENT COAL FORMATIONS.
We cannot properly close this geological sketch of the rocks of the earth and the place of coal among them, without referring to the coal formations of a later date than our true carboniferous coal measures. Of those later formations we have several deposits in Virginia and North Carolina.
The pakeozoic strata of this continent are rarely overlaid by the more recent formations, except in the western and less explored portions; while in England we find the new red sandstone and magnesian limestone imme diately overlaying the coal. It has been reported that we have a small coal formation known as the Permian,—which belongs geologically immediately above the true coal measures,—over the coal of one or two of our western fields. Most of our new or late deposits lie along the ocean belts and amid the oldest rocks of the earth. Thus, for instance, we find the Jurassic coals of Virginia and North Carolina deposited in or on the granite and gneiss rocks of those States.
The Jurassic is of later date than the Permian and Triassic, and nearly cotemporary with the Oolitic.
In order to embrace a full stratigraphieal view of Ameri can geology, we give an illus tration of the formations fol lowing the palmozoic in order. This column, it will be observed, rests on the granite,—an un usual and perhaps anomalous position,—but nevertheless re presents the true status of those formations. The Jurassic contains the coal of Richmond and Deep River, while the formations resting in the order of their age above it, are all deposits of a late period, and, in this county, are generally found resting on the older rocks which now bound these ocean shores.
We will merely notice those Jurassic or recent coal-fields in the present connection, reserving an extended description for its appropriate place in the ensuing pages.
The RICHMOND COAL-FIELD lies on or in a deep—perhaps volcanic— depression in the granite. It is about thirty miles long by five miles wide, and contains one hundred and eighty square miles of coal formation.
The depth of the basin is about one thousand feet; the average thickness of its coal is about twenty-four feet. It is highly bituminous and gaseous, disintegrates readily in the atmosphere, and is liable to spontaneous com bustion.
The PIEDMONT COAL-FIELD is on the Appomattox, in Prince Edward and Cumberland counties, Virginia, ranging in a northeast and southwest direction from the Roanoke to the James. The formation rests on the gneiss, and is frequently cut and interrupted by trap dikes. The coal bearing strata are, perhaps, not more than twenty miles long by three miles wide, containing an area of less than twenty square miles of coal. It con tains seven or eight seams, ranging from six inches to three feet in thickness, and not more than nine feet of workable coal, of a sulphurous and earthy nature.
The DAN RIVER COAL-FIELD has yet no fixed location or name. It extends from Leakesville to Germantown, a distance of thirty miles, in the same general northeast and southwest direction. The formation is in the vicinity of the gneiss, but is, we believe, underlaid by sandstones and slates. The coal is semi-bituminous, and contains specimens similar to the Pennsylvania anthracites. The seams are limited and small. We take this to be a continuation of the Piedmont basin.
The DEEP RIVER COAL-FIELD of North Carolina rests unconformably upon the mica slates of the gneissic period, and the material making up the formations is chiefly derived from the gold belt in the immediate vicinity. The area underlaid with coal is about forty-five square miles. Five seams of coal exist, the main one being from five to six feet thick.
We may merely mention here the existence of other mineral combusti bles, such as lignite, &c., which are found in still more recent formations ; but, as we do not propose to devote much time or space to their consider ation, it is not advisable to extend this geological sketch for the purpose.