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 

 between the years 1785 and 1790, a fallen tree displayed fragments 



