1847.] LYELL ON THE COAL-FIELD OF EASTERN VIRGINIA, 273 



a very regular concretionary and spheroidal structure on exposure to 

 the air. About 200 yards north of the great coke-pit, the trap, 14 feet 

 thick, is found within 26 feet of the surface. At the distance of about 

 two miles south of Townes and Powell's, at Crouch's pits, 300 feet 

 deep, where no trap occurs, the coal is bituminous and unchanged. 



Analysis of the Coke. — It will be seen by the table before given 

 (p. 270), that Mr, P. H. Henry, who has very carefully analysed 

 this coke, finds it to contain, carbon 86' 54, hydrogen 4' 23, oxygen 

 and nitrogen 4*53, ash 4*70. He informs me that, according to 

 Mr. Regnault, Welsh anthracite contains only 3*3 per cent, of hydro- 

 gen, and it appears in the paper before cited (Quart. Journ. Geol. 

 Soc. vol. i. p. 199), that Dr. Percy found only 2'45 per cent, of hy- 

 drogen, in the Pennsylvanian anthracite, which I submitted to his ex- 

 amination, from the Mauch Chunk mines. In the Frostburg coal 

 (see same paper), the total quantity of volatile ingredients (hydrogen, 

 oxygen and nitrogen) does not greatly exceed that detected in the coke 

 of Edge-hill, or Townes and Powell's, although the latter is so much 

 less inflammable. 



Mr. Mitchell, in his ' Geology of North Carolina' (1842), p. 133, 

 observes, that the theory of the fluviatile origin of the sandstone of 

 North Carolina (which, like that of East Virginia, contains coal) is 

 open to this objection : " That it takes no account of the trap, which 

 is not only imbedded in it, but traverses the sandstone in a thousand 

 different directions. The same trap (he adds) is not met with in the 

 slates and granite which lie adjacent to the sandstone, and the area 

 of a river or estuary could not have been liable throughout its whole 

 extent in length and breadth to injections and eruptions of trap, 

 whilst nothing of the kind occurred upon its banks." The same 

 might be said of the red sandstone districts of the valley of the Con- 

 necticut and of New Jersey, for there also we no sooner pass the 

 limits of the sedimentary strata and enter on the hypogene region, 

 than all the conspicuous masses of trap cease to show themselves. 

 But the explanation of this pheenomenon has probably occurred to the 

 mind of every experienced geologist. The same greenstone which 

 alters the coal at Clover-hill, above alluded to, crosses in the form 

 of a narrow dike through the adjacent hornblende schist ; and Mr. 

 Percival of Newhaven pointed out to me in 1842 several trap dikes 

 in Connecticut traversing the mica schist which forms the western 

 border of the *' new red sandstone" district of that State. I saw 

 other dikes to the eastward of the same region, east of Newhaven ; 

 and if they are not everywhere traceable, it arises from the wide extent 

 and depth of the '* drift" or ancient allu\dum which everywhere 

 overspreads the hypogene formations. The apparently abrupt cessa- 

 tion of the volcanic rocks, when we enter the granitic area, arises from 

 the more compact and crystalline form which they assume where they 

 have been consolidated in fissures which were deep-sited originally, 

 before the denudation of the country exposed the hypogene forma- 

 tions to view. Under such circumstances the narrow dikes of more 

 modern igneous rocks are scarcely distinguishable from some mem- 

 bers of the older and accompanying plutonic family, and they no- 



