CHAP. XV.] THICKNESS OF COAL-SEAMS. 213 



A great number of fossil fish, chiefly referable to two nearly 

 allied species of a genus very distinct from any ichthyolite hith 

 erto discovered elsewhere (a ganoid with a homocercal tail), 

 occur in the lower strata, with a few shells ; but they afforded 

 me no positive characters to determine whether the deposit was 

 of marine or fresh-water origin. Above these fossiliferous beds, 

 which probably never exceed 400 or 500 feet in thickness, a 

 great succession of grits, sandstone, and shales, of unknown depth, 

 occur. They have yielded no coal, nor as yet any organic re 

 mains. No speculator has been bold enough to sink a shaft 

 through them, and it is believed that toward the central parts of 

 the basin they might have to pass through 2000 or 2500 feet 

 of sterile rocks before reaching the fundamental coal-seams. 



The next ideal section will show the manner in which I sup 

 pose the coal-field to be placed in a hollow in the granitic rocks, 

 the whole country having suffered by great denudation, and the 

 surface having been planed off almost uniformly, and at the same 

 time overspread by a deep covering of gravel with red and yellow 



Section showing the Geological Position of the James River, or East Virginian 



Coal-Field. 



Fig. 4. 



A. Granite, gneiss, &c. B. Coal-measures. 



C. Tertiary strata. D. Drift or ancient alluvium. 



clay, concealing the subjacent formation from view, so that the 

 structure of the region could not be made out without difficulty 

 but for artificial excavations. It will be seen by the section 

 that the tertiary strata first make their appearance at Rich 

 mond about thirteen miles from the eastern outcrop of the coal, 

 and they continue to occupy the lower country between that city 

 and the Atlantic. 



The only beds of coal hitherto discovered lie in the lower part 



