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File:Geology of the Richmond Basin 1899 Plate XXXII.jpg

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English: Plate XXXII from The Geology of the Richmond Basin published by USGS, which has the following caption:
Structure of the Midlothian District. (After Clifford.)
The text of the report refers to the figure as follows:
The Clifford view (1888).—Mr. William Clifford, M. E., published an account of his observations upon the geology and methods of mining in the Richmond and Deep Run areas. He describes the coal measures as deposited in a huge hollow, probably 3,000 feet deep, having a length of 30 miles and a width of from 4 to 10 miles. The detached areas on each flank he speaks of as occupying hollows scooped out of the granitic rock, or as formed by the junction of ridges whose summits have been eroded, or by the local subsidence of the underlying granite. The author favors the hypothesis of original depressions, for he infers that the strata thin toward the sides of the basin as though the deposits had slidden down slopes on which they accumulated. Thickening toward the middle of the basin is held as the cause of flat strata in that part of the field.
The disturbances of the bed are described as waving longitudinal "ledges" separating the basin into more or less regular zones. These are traceable on the floor and roof alike of the coal measures.
He concludes that there is no evidence to show the nonoccurrence of the coal beneath the middle of the basin. The failure to find workable beds of coal in the "Sinking shaft" at Midlothian, described by Heinrich, he attributes to the bore hole not reaching the depth at which the coals should appear. He supposed that the strata at Midlothian continued to dip westward at about 25° at least to the vicinity of the "Sinking shaft." (See map, Pl. XXVI, and section, Pl. XXXII.) His theoretical section is based upon this conception of the structure, with marginal thinning.
Date
Source Nathaniel Southgate Shaler and Jay Backus Woodworth, 1899. Geology of the Richmond Basin, Virginia. U.S. Government Printing Office. United States Geological Survey.
Author USGS

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