40 J. J. STEVENSON — PENNSYLVANIA ANTHRACITE. 



Page 



Objections to Hypotheses of Murchison and Owen 57 



Objections to Lesley's Hypothesis . . « ..... 58 



Increased Rock-covering not productive of increased Heat 58 



' No increased Rock-covering in anthracite Region 58 



Increased Rock-covering not found to produce Anthracite 60 



Objections to Hypothesis of mechanical Force transformed into Heat 61 



Mallet' s Investigations 61 



Evidence of the Virginia Coals. 61 



Evidence of the Arkansas Coals 62 



Metamorphism not a sufficient Explanation of the Phenomena 62 



Bischof 's Theory of the Formation of Anthracite 63 



Lesley' s Suggestion of Oxidation 63 



Objections to Lesley's Suggestion 64 



Undisturbed Areas furnish all Varieties of Coal 64 



Influence of Glay-beds insignificant 64 



Process of Conversion completed prior to Rock-consolidation 64 



The Writer's Hypothesis as to Origin of Coal-beds 66 



Application of the Hypothesis ' .... 66 



Thickness of Coal greatest in northeastern Portion of Appalachian 



Basin 66 



Conversion greatest in the northeastern Portion of Appalachian Basin. 68 

 Relation of increasing Thickness of Coal to decreasing Volatile in Pennsyl- 

 vania 69 



Conclusions 69 



Introduction. 



Tables of analyses of coals from the Pennsylvania bituminous areas 

 show that the proportion of volatile combustible matter decreases toAvard 

 the east, though the rate of decrease is not regular and differs in the dif- 

 ferent beds. The decrease is ev^en more marked in that portion of the 

 state lying eastward from the bituminous areas, for there one finds the 

 passage from semi-bituminous to the hard dry anthracite of the Middle 

 fields. 



Pennsylvania Coal Areas. 



general extent. 



A general knowledge of the features and relations of the several coal 

 fields or geologic basins in Pennsylvania, as well as of their extensions 

 toward the south, is absolutely essential to an intelligent discussion of the 

 cause of the decrease in volatile. The portions of these basins or areas 

 lying within Pennsylvania Avas described by Professor H. D. Rogers in 

 his final report on the geology of the state, to which the reader is referred 



