244 ANTHRACITE COAL MEASURES. 



then have the coal as it actually exists, both upon 

 the hills and in the valleys, forming at times a por- 

 tion of the strata of the mountains, and only occa- 

 sionally lying in a basin form between the ridges. 

 Lying nearer the transition and primitive rocks, 

 w^hich are now universally allowed to have been 

 once either in a melted state by fire, or subjected 

 to great heat when the superincumbent strata were 

 upraised, forming hills and mountains, we. thus ac- 

 count for the fact that the coal of these strata 

 contain no bitumen, it having been dissipated by 

 the heat, while the bituminous coal measure lying 

 higher up in the series escaped its effects. To the 

 same purpose Dr. Hildreth remarks, that "there 

 seems to have been three different deposites of 

 coal throughout the main coal-region of the west. 

 After the vegetable materials which form the coal- 

 bed were deposited or buried under the superincum- 

 bent strata, it would seem that a strong degree of 

 heat had been applied, in addition to the pressure, 

 before they could assume their present bituminized 

 appearance. As we approach the coal-beds in the 

 transition and primitive rocks, the evidences of heat 

 are still more apparent, removing from the anthra- 

 cite beds all, or nearly all, their bituminous con- 

 tents, and in the primitive changing anthracite into 

 graphite or plumbago, which is almost pure car- 

 bon. 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 semi-metallic appearance, and it is often 

 produced in the furnaces of the arts by the action 

 of heat upon carbon." The theory that anthracite, 

 graphite, and bituminous coals are all of vegetable' 

 origin, and owe their present form to different de- 

 grees of heat and pressure, is in the highest degree 

 rational, and well supported by facts. 



