262 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [April 14, 



Before I discuss the question of the relative age of the strata, I 

 shall proceed to describe briefly the geographical extent, position, 

 and geological structure of the coal-field. The tract of country oc- 

 cupied by the crystalline or hypogene rocks which runs parallel to 

 the Alleghany mountains, and on their eastern side, is in this part of 

 Virginia about seventy miles broad ; in the midst of this space the 

 coal-field occurs in a depression of the granitic and other hypogene 

 rocks on which the coal rests, and by which it is surrounded along 

 its outcrop. The length of the coal-field from north to south is 

 about twenty-six miles, and its breadth varies from four to twelve 

 miles. It extends over portions of six counties, from Amelia the 

 most southern, through parts of Chesterfield, Powhatan, Henrico, 

 Goochland and Hanover. The James River flows through the middle 

 of it, about fifteen miles from its northern extremity, while the Ap- 

 pomattox River traverses it near its southern borders ; on its eastern 

 side it is distant about thirteen miles from the city of Richmond, the 

 capital of the State of Virginia : it occupies an elliptical area, the beds 

 lying in a trough, the lowest of them usually highly inclined where 

 they crop out along the margin of the basin, while the strata higher 

 in the series, which appear in the central parts of the basin, are very 

 nearly horizontal. The general strike is about N.N.E. and S.S.W., 

 while that of the nearest ridges of the Appalachian chain is about 

 N.E. and S.W. 



A great portion of these coal-measures consists of quartzose sand- 

 S Stone and coarse grit, some of the beds in the lower part of the series 

 "^ resembling granite or syenite, being entirely composed of the detritus 

 of the neighbouring granitic and syenitic rocks. Dark carbonaceous 

 shales and clays, occasionally charged with iron ores, abound in the 

 proximity of the coal seams, and numerous impressions of plants, 

 chiefly ferns and Zamites, are met vnih in shales, together with 

 flattened and prostrate stems of Calamites and Equisetum. These 

 last however, the Calamites and Equisetum, are very commonly met 

 with in a vertical position, more or less compressed perpendicularly. 

 That the greater number of Calamites standing erect in the beds 

 above and between the seams or beds of coal which I saw at points 

 many miles distant from each other, have grown in the places where 

 they are now buried in sand and mud, I entertain no doubt. This 

 fact would imply the gradual accumulation of the coal-measures 

 during a slow and repeated subsidence of the whole region*. 

 ii The coal-seams have hitherto been all found at or near the bottom 

 of the series, and the plants in beds below or between them, or im- 

 mediately overlying. One or two species of shells (Posidonomya ?) 

 also occur in the same part of the series, at a small height above the coal- 

 seams, and above these a great number of fossil fish chiefly referable to 

 -two nearly allied species of a genus very distinct from any ichthyolite 



* It is worthy of remark, that the Equisetum columnare, the same species as 

 that found in the Virginian coal-field, also occurs in an upright position, and ex- 

 tends over a wide area in those oolitic strata near Whitby in Yorkshire, which are 

 supposed, from the general evidence of the fossil plants, to be the equivalents in 

 age of these secondary coal-measures of America. 



