GEOLOGICAL SOCIETY OF PENNSYLVANIA. 



281 



Two or three coal beds or seams of variable thickness 

 comprise from 11 to 40 feet. 



For the details of the respective thicknesses of these 

 strata, and for a view of a complete suite of specimens 

 of every bed enumerated in the section, by which means 

 it was compiled; we are indebted to the liberality of Mr 

 Reid, the managing proprietor of these mines. 



These grits, and some of the shales, appear to have 

 originated solely in the destruction of primitive rocks, 

 and the whole series of these mechanically formed strata 

 is especially remarkable for the abundant prevalence of 

 mica, and at intervals of carbonaceous particles.* 



Some unimportant variations in the quality and thick- 

 ness of these superincumbent beds, as might be expected, 

 are noticed by those who have been employed in sink- 

 ing the deep shafts within this area, but the prevailing 

 character of the whole groupe remains unchanged. 



Whether any other groupe of rocks of this character 

 exists elsewhere, particularly under similar circum- 

 stances, filling up a deep granite basin, is unknown to 

 the writer. They are totally dissimilar to any other 

 rocks usually accompanying coal, whether transition or 

 secondary, that have come under the writer's observa- 

 tion on either side the Atlantic. f 



Coal, 



So great an accumulation of bituminous coal, almost 

 in one solid seam, as is presented in the Chesterfield 

 pits, is a highly interesting geological fact, without a 

 parallel in this continent. 



* Some of these carbonaceous white grits are quarried in large masses on 

 the borders of the James river canal, and are conveyed down to Richmond. 



t It is remarkable that they should" be deemed, by so experienced an ob- 

 server as M'CIure, to be allied to the old red sandstone, to none of the mem- 

 bers of which they bear any resemblance, and whose eastern and nearest 

 escarpment is 120 miles to the westward. 

 I.— 2 L 



