48 J. J. STEVENSON PENNSYLVANIA ANTHRACITE. 



forming a regular series to bituminous coal with very high percentage of 

 volatile.* 



HYPOTHESES AS TO CAUSES OF VARIATION. 



Rogers's Hypothesis. — The first elaborate. discussion was that presented 

 by Professor H. D. Rogersf at the third meeting of the American Asso- 

 ciation of Geologists. He states that " there prevails a very interesting 

 law of gradation in the quantity of the volatile matter belonging to the 

 coal, as we cross the Appalachian basin from the southeast to the north- 

 west." This law involves '' a progressive increase in the proportion of 

 the volatile matter, passing from a nearly total deficiency of it in the 

 driest anthracites to an ample abundance in the richest coking coal." 

 ' This conclusion is based upon '' a multiplied chemical analysis " and is 

 regarded as applicable to the whole region betAveen the northeastern 

 termination of the Coal Measures in Pennsylvania to the latitude of 

 Tennessee. 



He describes the several basins and discusses the character of the coal 

 in each. 



First. '' The southeastern chain of basins," answering practicall}^ to 

 the region between the Alleghany and the Kittatinny, but embracing at 

 least part of the Great valley in Virginia. Here he finds the coal to be 

 anthracite for the most part, with some slightly bituminous fields as 

 Broad Top and the areas in Virginia, the volatile varying from 6 to 12 

 or 14 per cent. 



Second. The well defined range of basins immediately northwest of 

 the Alleghany mountain in Pennsylvania, the Potomac basin in nearly 

 the same line and the coal-fields of Big and Little Sewell mountains on 

 the Kanawha and lower New river of West Virginia. The undulations 

 are broad and gentle, the region being wegt of steep flexures and beyond 

 all considerable dislocations. The volatile varies from 16 to 22 per cent. 

 This includes the first and second bituminous basins of Pennsylvania. 



Third. The great Appalachian basin, which includes the third and 

 remaining bituminous basins in Pennsylvania, as well as their southern 



* Professor Persifor Frazer has shown (Trans. Amer. Inst. Mining Engineers, vol. vi, ) that it is 

 impossible to compare coals unless the impurities be ignored. He recommended a i-eturn to 

 the method used by Professer Johnson many years ago, in which the ratio between the volatile 



and the fixed combustible matter was used as the basis of comparison. The formula is 



V xx — C 



the fixed carbon divided by the volatile hydrocarbon. Thus the grouping becomes — 



Hard dry anthracite 100 to 12 



Semi-anthracite 12 to 8 



Semi-bituminous 8 to 5 



Bituminous 5 to 



t Rogers: Reports of the First, Second and Third Meetings of the Association of American 

 Geologists and Naturalists, 1813, p. 470 et seq. 



