HYPOTHESES AS TO VARIATION IN VOLATILE. 49 



extension in West Virginia, Ohio and Kentucky. The folds are gent'e 

 and the bituminization increases northwestward from 31 per cent, atth • 

 southeast to 40 or 43 per cent, near the western side of Pennsylvania 

 and on the Kanawha river in West Virginia. 



The variation in degree of bituminization of the coal in different por- 

 tions of the region is attributed to the prodigious quantity of intensely 

 heated steam and gaseous matter escaping through crevices necessarily 

 produced during the permanent bending of the strata. The elevation of 

 the coal rocks must have been accompanied by the escape of an immense 

 amount of hot vapors, whose influence cannot be overlooked upon any 

 hypothesis of the rending and elevation of great mountain tracts. The 

 coal throughout the eastern basins, if thus effectually steamed, would 

 discharge more or less of its volatile constituents as the strata were more 

 or less violently undulated by earthquake action. The more western 

 beds, more remote from the scene of violent action, less crushed and 

 broken, would be less extensively debituminized. 



The entire absence of true eruptive rocks in the anthracite fields, 

 which might have caused the change, is a circumstance which lends 

 great support to this theory. The bitumen in the coal augments west- 

 ward, precisel}^ as the flexures diminish. No such law of gradation 

 could result from transmission of heat from the general lava mass below 

 the crust, for that would involve a corresponding increasing gradation 

 in thickness of crust westward, which is in conflict with the diminishing 

 thickness of Appalachian rocks westward and contrary to correct geo- 

 thermal considerations. , 



Professor Rogers resumed the discussion in his final report,* and gave 

 additional matter respecting the variation of volatile in the anthracite 

 basins. The increase of volatile is not along a northwest and southeast 

 line, but along an east and west line, '" or, perhaps, more exactly, toward 

 the west-northwest." The occurrence of semi-anthracite as well as of 

 semi-bituminous coal in the Southern anthracite field is described. The 

 absence of semi-bituminous in the other anthracite fields is accounted 

 for by the fact that they do not extend far enough to the westward, 

 reaching, as they do, barely to the line of semi-anthracite in the Southern 

 field. There is a decided increase in volatile westward in these fields.f 

 The intensely anthracitic condition at the easterly end of the basins is 

 accounted for by proximity to the region of dikes, which are especially 

 numerous between the Delaware and Schuylkill rivers, but less abun- 

 dant between the latter stream and the Susquehanna. Professor Rogers 

 calls attention to the cracked or jointed condition of the coal as affording 

 means for rapid escape of the ^aseS: 



* Rogers : The Geologj' of Pennsj'lvauia, vol. 2, 1858, p. 995 et seq. 

 fThis, it must be remembered, is in the direction of trend. 



