64 J. J. STEVENSON — PENNSYLVANIA ANTHRACITE, 



OBJECTIONS TO LESLEY'S SUGGESTION. 



Undisturbed Areas furnish all Varieties of Coal. — If we had to deal only 

 with the extremes, with the rich gas-coal of the Pittsburg area and the 

 dry anthracites of the Middle anthracite fields, these suggestions would 

 have greater weight ; but we must remember that the practically undis- 

 turbed or only gently folded beds of the bituminous basins west from the 

 Alleghany mountain yield every possible gradation, from the richest bitu- 

 minous coals to the semi-anthracites of the Loyalsock (Bernice) field, the 

 latter having in some cases even less volatile than the Lykens valley coals 

 of the Southern anthracite field. In all of these are found the clay-beds 

 which should prevent percolation and the rest ; but it is unnecessary to 

 go outside of the anthracite field for an illustration, for in a single colliery 

 on the Mammoth bed in the Southern anthracite field semi-bituminous, 

 almost bituminous, coal occurs in one bench and hard anthracite in 

 another, the ratios being 5.59 and 51.1.* 



The Northern anthracite field, as described by Chance and by Ash- 

 burner, is not fractured. It seems to be much less disturbed than is the 

 southern portion of the Broad Top semi-bituminous field. Ashburner's 

 sections show a good deal of clayey material. Taken all in all, the condi- 

 tions in Broad Top appear to be more favorable to percolation and 

 oxidation than are those in the Northern field, certainly far more favor- 

 able than those in the Loyalsock field, if extent of fracturing and thick- 

 ness of clays be the test. 



Influence of Clay-beds insignificant. — The presence or absence of the clay- 

 beds evidently has very little to do with the matter. Ashburner's sec- 

 tions in the Northern field show more clay-beds than can be found in a 

 greater thickness of rock within the Black mountain coal-field of south- 

 west Virginia, immediately behind the overturned anticlinal of Stone 

 mountain ; yet at half a mile from the vertical beds in that fold the 

 Imboden bed shows a fuel ratio of 1.67, while the Kelly bed, at barely a 

 stone-throw from the vertical beds, has a fuel ratio of 1.48. Certainly 

 this area should be cracked-up enough, for its southeasterly boundary is 

 the Stone mountain anticlinal and the faulted area of southwest Virginia, 

 while its northerly boundary is an enormous fault. An even more satis- 

 factory illustration is found in the southeastern prong of the Southern 

 anthracite field, where, within a dozen miles along the trend, the ratio 

 varies from 4.64 to 12.40. 



Process of Conversion completed prior to Rock-consolidation. — The sugges- 

 tion immediately under consideration evidently carries with it the addi- 

 tional suggestion that the change was not complete even when the whole 



*A. S. McCreath : Ann. Rep. of Second Geol. Survey of Pennsylvania for 1885, p. 321. 



