264 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [April 14, 



of coal in the soil adhering to its roots, which led to excavations, and 

 the discovery, at the depth of a few yards, of a rich bed of bitu- 

 minous coal, no less than 30 feet thick, of excellent quality. Being 

 so near the surface, it was for a time worked with great profit ; but 

 very exaggerated notions were formed, both here and in the vicinity, 

 of the real thickness of the main seam, due allowance not being made 

 at first for the dip of the beds through which the shafts passed down 

 obliquely to the planes of stratification. In the valley of a small 

 tributary of the James River, about two miles north of Blackheath, 

 I saw, exposed in a natural section of drift, a bed of rubbly coal, 

 which might easily have betrayed the existence of the seam from the 

 waste of which it had been derived. 



It has been usually stated in reports on this coal-field, that north 

 of the James River the coal is divided into two or three seams, while 

 to the south of the same river it forms one huge seam from 30 to 40 

 feet thick. Such however is not the case, the coal being almost every- 

 where separated into three distinct beds, and sometimes more, and 

 this division being observable quite as much in the southern as in the 

 northern half of the trough. The uppermost seam is almost always 

 the most important. Thus in the Clover-hill pits, near the Appo- 

 mattox River, towards the southern extremity of the basin, I found 

 five seams of coal, all as usual at the margin of the basin. Here, 

 about 160 feet of grit and shale intervene between the lowest of the 

 five seams and the fundamental granite and hornblende schist. Of 

 this section I shall have to say more in the sequel. In all the loca- 

 lities I visited, the thickest bed of coal or the main seam is the upper- 

 most, except at Clover-hill just mentioned, where a thin layer of coal 

 is met with still higher ; but it is not continuous for any distance. 

 Along the western margin of the basin at Dover, for example, I ob- 

 served the same division of the coal into two or more seams ; nor am 

 I aware of any place, except Blackheath and the adjoining parts of 

 Chesterfield county, where all the seams appear united as it were into 

 one, of unusual strength, from 30 to 40 feet thick, — to explain which 

 we may perhaps adopt the theory of Mr. Bowman, and suppose the 

 vegetation to which the coal is due to have grown uninterruptedly in 

 this spot, while elsewhere it was frequently arrested for a time in its 

 progress by subsidence, which submerged certain areas and permitted 

 the deposition of mud and sand to take place upon the materials of 

 the future coal. This unity however of the coal-seam in the Black- 

 heath region is of small extent, and even in the purest mass there 

 occur thin intercalated layers of shale and sandstone with pyrites, to 

 separate which from the coal costs the miner no small labour. These 

 "partings" of sedimentary matter, which in some spots swell out 

 rapidly from a few inches to a thickness of several feet, or even yards, 

 make the great seam of Blackheath much less of an exceptional case 

 in a geological point of view than might at first be supposed. The 

 inconsiderable distance to which the undivided state of the seam ex- 

 tends, is shown by the section obtained only a quarter of a mile to the 

 south of Blackheath in the Midlothian pits, where a shaft sunk to the 

 depth of 774 feet passed through the undermentioned beds. 



