50 J. J. STEVENSON — PENNSYLVANIA ANTHRACITE. 



Oioeii's Hypothesis. — The occurrence of anthracite coal in Arkansas 

 among undisturbed rocks and at 60 miles away from the nearest igneous 

 rocks led Dr D. D. Owen* to surmise that the heat necessary for the 

 conversion of bituminous coal into anthracite must have been derived 

 from " granite and other hypogene (nether-born) rocks " near enough the 

 surface to have permeated the strata with heated vapors or gases, which 

 expelled the greater part of the gaseous matter, or else the coal has been 

 subject to some extraordinary chemical agency by which CH^ has been 

 removed. He cannot think that the Spadra coal, so different from that 

 only a few miles further west, can owe its present composition to any 

 difference in the vegetation. Its " peculiar fissured structure favors the 

 idea that the volatile matter has been expelled by a process more rapid 

 than can be attributed to slow chemical changes, unaided by an eleva- 

 tion of temperature." 



Stevenson'' s Hypothesis. — In 1877 J. J. Stevenson,t discussing the varia- 

 tions of volatile shown by the Pittsburg coal-bed in southwestern Penn- 

 sylvania and the adjacent portion of West Virginia and Maryland, 

 antagonized the theory that debituminization of the coal toward the 

 southeast is due to increased disturbance in that direction. He showed 

 that there is practically no increase in extent of disturbance from the 

 first subdivision of the third bituminous basin southeastward to the first 

 bituminous basin, so that heat clue to the transformation of mechanical 

 force cannot be regarded as the cause to which the debituminization is 

 due. He gave illustrations of noteworthy changes in structure of the 

 coal-bed eastward in the several basins, and concluded that the difference 

 in volatile is due to difference in conditions under which the coal was 

 formed. 



Lesley''s Hypothesis. — In 1879 Professor J. P. Lesley| inserted a discus- 

 sion of this question into Mr A. S. McCreath's second report on the 

 chemical work of the survey. In this he tabulated the analyses pre- 

 sented by Mr McCreath in the previous pages and, after comparing them, 

 offered some suggestions, each of which deserves serious consideration. 



He suggests, first, that the percentage of fixed carbon ought to increase 

 with depth of tlie coal beneath the surface, for the earth's temperature 

 increases one degree Fahrenheit for every 50 or 60 feet of depth. In 

 western Pennsylvania, however, under present conditions, the effect of 

 this increment in temperature must be insignificant, as the lowest coal- 

 bed, the Sharon, is but 1.600 feet below the Washington, the highest of 



*Owen: First Report of a Geological Reconnaissance of the northern Counties of Arkansas, 

 1858, p. 131. 



t Stevenson : Second Geol. Survey of Penn., Report of Progress in the Fayette and Westmoreland 

 District, etc., part i, 1877, p. Gl et seq. 



t Lesley : Second Geol. Survey of Penn., Second Report of Progress in the Laboratory, etc., 1879, 

 p. 153 et seq. 



