272 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [April 14, 



not extended to lower seams. In fact, at Duval's and farther north, 

 at Townesand Powell's pits, the trap overlies the coal, and forms a 

 bed having the same dip as the coal-bearing strata. 



At the -first-mentioned of the above places (Duval's pit, on the 

 south bank of the James River), a shaft, open at the time of my visit, 

 had passed through — first, 1 05 feet of sandstone and shale, then the 

 greenstone reduced to a thickness of 6 feet and parallel to the strata. 

 Below the trap, strata 25 feet thick, similar to those above, were met 

 with, and then the main seam of coal 10 feet thick, of which the 

 quality was not affected as in some adjacent mines, owing probably to 

 the thinness of the greenstone and the interposition of the other rocks. 

 Below the coal the miners entered black slaty rocks 35 feet thick with 

 numerous prostrate and upright Calamites, and then reached a second 

 bed of coal 3 feet thick of excellent quality resting on other carbona- 

 ceous slates with Calamites. Next came the bottom coal 6 feet thick, 

 also unchanged : some other thin partings of coal between this bed 

 and the fundamental granite, show how various are the modifications 

 under which the seams of coal present themselves, — a diversity proba- 

 bly connected with the variations in the amount of the subsidence to 

 which the erect position of the Calamites observed at intervals over 

 so wide an area clearly points. 



Coke of Townes and PowelVs Pits. 



The niost remarkable example of natural coke met with in this or 

 any other coal-field known to me, occurs at Townes and Powell's pits 

 at Edge-hill, a locality between five and six miles north of the James 

 River and ten north of Blackheath, being also on the eastern outcrop 

 of the basin and within 500 yards of the granite. A large quantity 

 of coke, used for furnaces and other economical purposes, is here ex- 

 tracted from a bed about 8 feet thick, below which at greater depth 

 are two beds of imperfect coal. The measures passed through above 

 the 8-feet-bed of coke are 110 feet thick, including a conformable 

 bed of blue basalt 16 feet thick. The shale immediately below the 

 trap was white for 1 1 feet, and then 25 feet of dark leafy shale succeeded, 

 below which came the bed of coke resting on white shale, and 

 lower down coal-measures with two seams of inferior coal, each about 

 4 or 5 feet thick. The shale, 47 feet thick, interposed between the 

 basalt and the coke, exhibits so many polished surfaces or slick ensides, 

 and is so much jointed and cracked, and in some places disturbed and 

 tilted (in one area of 12 feet the beds being vertical), that we may 

 probably attribute the change from coal to coke, not so much to the 

 heating agency of the intrusive basalt, as to its mechanical effect in 

 breaking up the integrity of the beds, and rendering them permeable 

 to water, or the gases of decomposing coal. In some places in the 

 same district where the upper part of a seam is coke, the lower is coal, 

 and there is sometimes a gradation from the one to the other, and 

 sometimes, I was told, a somewhat abrupt separation. The general 

 dip of the strata in this locality is W.S.W. Calamites are abundant 

 in the beds associated with the coke. 



I observed that some of the basalt of the neighbourhood assumed 



