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 



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