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ON THE AGE OF THE 



On the Age of the Coal Rocks of Eastern Virginia. By 

 William B, Rogers, Professor of Natural Philosophy in the 

 University of Virg'inia. 



The formation here referred to, overspreads parts of Chester- 

 field, Powhatan, AmeUa, Henrico, Hanover, and Goochland 

 counties, lying in basins of gi-anite and gneiss, the principal coal 

 seams being separated by only a few feet, and sometimes by but 

 a few inches, of carbonaceous shale from the floor of primary rock. 

 In some places near the eastern margin of the field, where it has 

 been most extensively explored, the thickness of this group of 

 strata is about eight hundred feet, but towards the centre of the 

 principal basin it is probably somewhat greater. Throughout 

 much of this depth the strata consist of coarse grits, composed of 

 the materials of gi-anite, so little worn as to have the aspect of this 

 rock in a decomposing state. The coal, which in the northern 

 parts of the field is divided into two and sometimes three distinct 

 seams, separated by considerable intervals of slates and grits, but 

 all comprised within the lowest one hundred and fifty feet of the 

 series, is in the more productive region, south of the James river 

 in Chesterfield county, collected together into one immense stra- 

 tum, which, though of very variable thickness, may be generally 

 stated at from twenty to forty feet.* 



The curious circumstance, of the grits and coal-bearing strata 

 of this region resting immediately on a floor of granitic and 

 gneissoid rock, appears early to have attracted notice, and, con- 

 nected with the fact, that the coarser sandstones are but the re- 

 cemented materials of the adjoining primary masses, almost 

 unmarked by aqueous wearing, seems to have led to the prevail- 

 ing belief of the very high geological antiquity of these deposits. 

 Such considerations, and others, chiefly lithological, would appear 

 to have formed the grounds upon which the distinguished pioneer 



* For a particular account of the boundaries and contents of this coal field, the compo- 

 sition of its numerous varieties of coal, and other details, see Reports of Geological Survey 

 of Virjrinia, for 1^30, 1S40. Also, " Memoir of a Section passing- through the Bituminous 

 Goal Field near Richmond," by Richard C. Taylor. A more copious and accurate account 

 will hereafter appear in the Final Report on the GeologT' of the Slate. 



