Formation of Coal, 125 



Where not removed by degradation, or buried under other strata, 

 there seem to have been three distinct deposits of coal throughout 

 the main coal region, embraced on the map, which accompanies these 

 observations. After the vegetable materials which form the coal 

 beds, were deposited or buried under the superincumbent strata, it 

 would seem that a strong degree of heat had been applied, in addi- 

 tion to the pressure, before they could assume their present bitumin- 

 ized appearance. As we approach the coal beds, in the transition 

 and primitive rocks, the evidences of heat are still more apparent ; 

 removing from the anthracite beds, all, or nearly all their bituminous 

 contents ; and in the primitive, changing anthracite into graphite, or 

 plumbago, which is almost pure carbon. It would appear, that we 

 cannot reasonably doubt the action of heat on these coals, for the 

 plumbago is evidently a coal, changed by heat into its present serai- 

 metallic appearance, and it is often produced in the furnaces of the 

 arts, by the action of heat upon carbon. A less degree of heat has 

 been apphed to the bituminous beds of " the valley of the Ohio," 

 for they are far removed from any crystalline or transition rocks, on 

 which the marks of heat are so apparent, and therefore could not 

 receive a sufficiency to deprive them of their bituminous principles 

 and change them to carbonaceous coal beds. The suggestion ad- 

 vanced by many geologists, and recently applied by Prof. Hitchcok, 

 in his geology of Massachusetts, that graphite, anthracite and bitu- 

 minous coals are all of vegetable origin, and changed by heat and 

 pressure to what they now are, is a simple and beautiful illustration 

 of a heretofore obscure and difficult subject. 



Minerals associated with the Coal. 



Sulphuret of iron is almost the only mineral found constantly as- 

 sociated with coal ; and this is more or less abundant in all the 

 beds — some possess it in large quantities, a thin stratum, often run- 

 ning for a considerable distance in the center of the deposit. It al- 

 so appears in thin veins between the seams of the coal, as for exam- 

 ple occupying only the thickness of the fossil leaf, which is replaced 

 by the sulphuret; and bearing on its surface, the ribs and nervures 

 in beautiful relief. Sometimes it is found between the laminae of 

 coal in filaments and dendritic fibres spreading out like the branch- 

 es of a tree, and with various colors Tesembling fine brass, gold and 

 silver. In coal banks, it is seldom or never, found in regular 

 crystals, but always assumes geometrical forms in beds of blue 



