292 



TRANSACTIONS OF THE 



degrees, and though partially interrupted by faults, is 

 found tp flatten towards the interior. 



Of these dislocationsj which are perceptible to a greater 

 or less extent in most of the coal pits within this area, it 

 is not now the intention of the writer to speak. Such 

 faults are to be expected so near the outcrop of these 

 highly inclined rocks. We will only advert to the most 

 remarkable line of fracture, which runs along the whole 

 eastern side of the coal field, throwing up the coal in 

 such a position as to form a double crop ; that is, two 

 distinct outcrops of the same seam. 



The Black Heath mines, the Union mine and the Deep 

 Run pits range along the outer strip or belt of coal, and 

 are separated entirely from the main area, by a step of 

 granite, miscalled a hill or wall. 



We have, therefore, the peculiar circumstance of a 

 double tier of shafts and collieries, running nearly parallel 

 with, and at no great distance from, and apparently co- 

 extensive with the entire mineral basin, yet perfectly 

 detached and separated by an interposing face or wall of 

 primitive rock, against which the outer rim of coal rests. 

 This fracture and subsidence are represented in our dia- 

 gram fig. 5, as accurately as the small scale of the section 

 and the obscurity of the data would allow. 



One other feature, and that unquestionably peculiar to 

 the Richmond coal region, remains to be adverted to. 

 It is the lowest in position in the United States, or, for 

 aught that is known to the contrary, in the whole conti- 

 nent ; being already worked to the depth of from 100 to 

 near 350 feet below the level of tide. 



Combining the various circumstances which have been 

 thus hastily and imperfectly sketched, it will be seen that 

 this area presents one of the most remarkable features in 

 American geology, in connection with the subject of coal. 



The only parallel to which I can with probability 

 refer it, is in the coal deposits of central France, which 



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