1847.] LYELL ON THE COAL-FIELD OF EASTERN VIRGINIA, 267 



and half a mile in breadth. The coal there is similar in quality to 

 that of Blaekheath, and I found the accompanying shales full of that 

 splendid fern, the Tceniopteris magnifolia, spread out between the la- 

 minae, as in the shales of Clover-hill at the southern end of the coal- 

 field. The same Calamites, Equisetum and Zamites also occur there, 

 and in nearly every locality, though some species of ferns have only 

 as yet been met with at one place, as for example the Filicites jim- 

 briatus (Bunbury) and Pecopteris hullata (Bunbury), which I found 

 at the Deep-run mines just mentioned, and Neuropteris linncEcefolia 

 found at Blaekheath. It is the opinion of some of the miners, that 

 where several seams of coal occur, they would form, if united, a single 

 seam, about equal in the aggregate to the average thickness of the 

 great single bed of coal in the Blaekheath region ; but it seemed to 

 me that the strength of the beds in most of the workings would never 

 approach in importance the single main seam in the Blaekheath and 

 Midlothian pits — and here also the seam is sometimes no less than 

 30 feet thick where other beds of coal intervene betv/een it and the 

 granite. This may be seen about two miles north of the Engine pit, 

 at the place where the coal was first obtained in 1785, in the valley of 

 a small tributary of the James River. The main seam is there 30 feet 

 thick at its outcrop, and in the coal-measures separating it from the 

 granite, consisting of grit and shale 200 feet thick, are seen two beds 

 of coal, the uppermost three feet and the lowest about one foot 

 thick. 



It was before stated (page 263), that there have been no borings 

 for coal in the central parts of the coal-field ; the only section I could 

 obtain of the beds far from the margin of the basin is that afforded 

 by the cuttings along the Richmond and Lynchbury canal, and these 

 are only a few yards in depth. The beds here consist of shale and 

 quartzose grit, one undivided stratum of which, ten feet thick, was 

 very conspicuous. 



Wherever I observed these strata closely, their dip was about 10° 

 south-east ; but on reaching the western outcrop of the coal at Dover, 

 only three-quarters of a mile from where the beds are so slightly in- 

 clined on the canal, I found the coal-measures dipping at an angle of 

 no less than 50° east, or opposite to that prevailing at Blaekheath on 

 the other side of the trough. The seams of coal at Dover correspond 

 very closely at their outcrop near the granite with those before men- 

 tioned, where the western dip prevails, the main seam at Dover being 

 1 6 feet thick, and there being two other thinner ones below. Only a 

 mile or two south of the open shaft at Dover, where I saw the beds 

 dipping at an angle of 50°, I observed the strata near the granite to 

 be almost horizontal. The same may be said of the strata three miles 

 south of the Powhatan pits, near their junction with the crystalline 

 rocks on the eastern outcrop. I was told also of instances of the strata 

 dipping towards the granite, as for example three miles south-east of 

 the Midlothian pits before mentioned. In short, the disturbances 

 have been so great, that although the general structure of the coal- 

 field is that of a basin or trough, as before stated, the deviations from 

 this form are numerous. 



