File:The Quarterly journal of the Geological Society of London (13206177714).jpg

1847.. LYELL ON THE COAL-FIELD OF EASTERN VIRGINIA. 2/1
Tract," a dike of greenstone is seen about 20 feet thick, running
W. 10° S. ; the coal-measures crop out here near the granite at various
angles between 10° and 45°. Near the locality last mentioned, I ob-
tained at the Beaver mine a section passing through five seams of
coal : see Section Fig. 5. The fundamental rocks consisted of granite
Section at Clover-hill, Virginia.
Fig. 5.
2 3 4
A. Granite.
B. Hornblende schist.
C. Coal-measures.
D. Dike of greenstone.
E. Drift, or ancient alluvium.
C 10 feet stratum of sandstone.
1, 2, 3. First, second, and third coal-seams.
4. Four foot coal.
5. Main seam of coal, 10 to 12 feet thick.
and hornblende schist, on which repose coal-measures, chiefly of white
sandstone and shale 500 feet thick with three seams of coal, the
uppermost of which was cut through by the dike of greenstone, the
coal, as the miners expressed it, having been burnt up by it and altered
into a kind of coke. On the altered coal No. 3 rests a solid undivided
stratum of sandstone 1 feet thick, and on this a seam of coal 4 feet
thick, to which succeeds slaty shale 30 feet thick, and on this rests
the fifth seam or main coal, 10 to 12 feet thick. Then follow strata
of sandstone, shale and other rocks without coal for a thickness of
about 160 feet, exposed continuously. The next point to the north
where I saw greenstone in connexion with the coal-measures was in
Salle's Tract, within a mile-and-a-half of the James River and near
the United States' Arsenal, about sixteen miles north of Clover-hill
pits last mentioned. In this region some of the coal is aifected and
more or less deprived of its bituminous qualities, although not in
contact with the igneous rock, which however I traced to within 1 20
feet of the altered coal, and it may approach much nearer.
Not far from the same locality, in "Burfoot's Tract," about three-
quarters of a mile from the Arsenal on the James River, the principal
coal-seam was described to me as damaged by the near approach to it of
the whin and a kind of coke produced. The mass of trap was visible, a
greenstone of the ordinary character 28 feet thick, and near it a brec-
ciated rock of hardened shale varied by patches of carbonaceous
matter resembling impure coke in appearance. The locality, like all
the others, is near the junction of the coal-measures and the granite.
Before visiting the Richmond or East Virginia coal-field, I had been
asked by some geologists, whether it was not a singular phsenomenon
that some upper beds of coal had been deprived of all their volatile
matter, while others below remained perfectly unaltered and bitumi-
nous? The explanation appears to be simply this: that the greenstone,
although intrusive, has often here, as is so common elsewhere, made its
way between the strata like a conformable deposit, and has driven out
the gaseous matter from the upper coal, while its influence has often