30 STEVENSON— INTERRELATIONS OF FOSSIL FUELS. 



His report, published in 1836, contained a brief statement which 

 adds important observations while confirming those made by Taylor. 

 He discovered that the overlying sandstone group apparently over- 

 laps the coal measures and that the lowest coal seam is separated 

 from the granite in most cases by only a few feet of shale. The 

 coal thickens toward the center of the basin and, as a rule, the 

 higher seams are the best. 



In the Midlothian and several adjacent mines, there is ample 

 evidence to prove that the coal accumulated in saucer-shaped basins 

 to the thickness of 40 or 50 feet, while on the eminences of the 

 same floor it is thin. On the south side of the James River, the 

 River pit was abandoned when the granite floor rose almost to the 

 sandstone roof. Near Tuckahoe, on the north side of the river, the 

 coal was found central in a small, isolated, cup-like depression. 

 This coal rose gently in all directions from the shaft and thinned 

 from 5 to 2 feet toward the edges of the shallow basin. This is 

 several hundred feet in diameter and its strata vary little from the 

 original nearly horizontal position. " Everything lends countenance 

 to the opinion that the surface of the primary rock, previous to the 

 deposition of carbonaceous matter, was a valley of rolling outlines, 

 occupied by hollows and elevations, causing the first layers of 

 matter, which were thrown down, to be deposited in greater thick- 

 ness in some places than in others. As the lowest coal seam is 

 separated from the crystalline rock by only a very few feet of shale 

 and in some cases by none at all, it appears likely that the distri- 

 bution of the coal was made unequal in thickness from the very 

 commencement." 



In his later memoir, discussing the relation of the plant remains, 

 Rogers stated that the most abundant plants are Equisetum 

 coliimnare, Tccniopteris, and a large species of Zamitcs. These 

 occur in vast numbers immediately upon the coal or interlaminated 

 with it. They are accompanied by Calamites, Pecopteris and Lyco- 

 podites. The Equisetum is so abundant, at times, as to give a coarse 

 coal consisting of alternate laminations of coal and shale with occa- 

 sionally 30 laminations to the inch. Ferns are rare, aside from the 

 great Tccniopteris. The only animal remains are those of fish and 

 some teeth supposed to be reptilian. The fish remains are in dark 



