File:The Quarterly journal of the Geological Society of London (13205983323).jpg

184/.. LYELL ON THE COAL-FIELD OF EASTERN VIRGINIA. 2(53
hitherto discovered elsewhere. Above these fossiliferous beds, which
probably never exceed 400 or 500 feet in thickness, a great succes-
sion of grits, sandstone and shales, of unknown depth, occur. They
have yielded no coal, nor as yet any organic remains, and no speculator
has been bold enough to sink a shaft through them, as it is feared
that toward the central parts of the basin they might have to pass
through 2000 or 2500 feet of sterile measures before reaching the
fundamental coal-seams.
Section showing the Geological Position of the James Rive?% or
East Virginian Coal-Field.
Fig. 1.
A. Granite, gneiss, Sec. B. Coal-measures.
C. Tertiary strata. D. Drift or m^cient ullmnum.
The annexed ideal section (1) will show the manner in which I suppose
the coal-field to be placed in a hollow in the granitic rocks, the whole
country having suifered by great denudation, and the surface having
been planed off almost uniformly, and at the same time overspread
by a deep covering of gravel and red and yellow clay, concealing the
subjacent formation from view, so that the structure of the region
could not be made out without difficulty but for the artificial excava-
tions. It will be seen by the section that the tertiary strata appear at
Richmond, about thirteen miles from the eastern outcrop of the coal,
and they continue to occupy the lower country between that city and
the Atlantic.
It has been stated, that the only beds of coal hitherto discovered
lie in the lower part of the coal-measures, and that consequently they
crop out all round the margin of the basin. As the dip is usually at
a considerable angle, vertical shafts from 400 to 800 feet deep are re-
quired to reach the coal at the distance of a few hundred yards inside
the edge of the basin ; it is only therefore along a very narrow band
of country that the coal comes up to the surface naturally, and even
here it is for the most part buried under superficial red and yellow
clay with sand and gravel, the whole often 30 or 40 feet thick. I
saw no erratic blocks or far-transported materials in the detritus, but
it is so continuous as to conceal the junction of the carboniferous and
granitic rocks, and I felt some curiosity to learn how the existence of
coal in such a country had been originally suspected. It appears
that in Chesterfield, the county where the richest seams occur, the
coal enters very largely into the composition of the overlying gravel
and sand, and at the old Blackheath pits, which were first worked