54 



is invariably the purest coal. We have thus, at a distance of nearly 

 10 miles from each other, two localities, showing sufficient corres- 

 pondence in the relations of the seams to each other and to the adja- 

 cent strata, to establish the continuity of the same beds across the 

 whole coal field. 



In some of the shafts on Tuckahoe creek, as many as five sepa- 

 rate seams have been struck, of thickness sufficient to justify work- 

 ing, and there exist many more of insignificant dimensions which 

 are neglected. There are good local reasons in several parts of 

 the coal field on the north side of the river for believing, that the 

 seams occasionally coalesce, so that two become but one. 



We do not conceive it essential to the objects of the present re- 

 port, to specify anything more respecting the local details of the 

 numerous mines in this coal field, than is requisite to make its im- 

 portance and peculiar structure understood. 



On the south side of the James river, an old mine, called the 

 River pit, now deserted, contained at the depth of 130 feet, a seam 

 of coal 20 feet thick, but which, owing to a close approach of the 

 granitic floor to the sandstone roof, was so reduced in thickness as 

 to be abandoned. 



Upon the east side of the same portion of the basin in Mills' 

 mines, the coal varies rapidly in thickness, from almost nothing to 

 upwards of 40 feet, and in one place to sixty feet, if we include thin 

 bands of the coal shale. In the Midlothian pit the shaft is 500 feet 

 in depth, and the workings are carried to the depth of 700 feet below 

 the soil. The coal is very variable in thickness, being worked 

 at more than 30 feet, and in some places it is even thicker. In this 

 mine, as in several of the adjacent ones, we have numerous instances 

 of the coal filling up hollows as it were in the floor, being accumu- 

 lated in saucer-shaped basins to the thickness of 40 or 50 feet, and 

 resting in comparatively thin masses upon the eminences in the same 

 floor. In some instances, these subordinate basins are almost en- 

 tirely insulated from the rest of the coal field, and are presented 

 under features which preclude us from supposing that they owe 

 their shape exclusively to the numerous faults which intersect the 

 strata. Upon the north side of the river near Tuckahoe, the coal was 

 reached precisely in the centre of a small insulated cup-shaped de- 

 pression. The coal as it was pursued, was found to rise gently on 

 all sides from the shaft, and also to thin away from a thickness of 

 four or five feet to two feet towards the edges of this shallow basin, 



