682 THE JOURNAL OF GEOLOGY. 



Professor Rogers's error in this matter prevented him from 

 observing that the volatile decreases northwardly along the 

 trend in the several basins even more notably than along the 

 line chosen hy him. The hardest anthracite is not in the 

 Southern field, where the folding is most complicated, but in the 

 Eastern Middle. The Southern Anthracite field shows all grada- 

 tions from bituminous coal at its southern extremity to hard, dry 

 anthracite at its northerly end. 



Professor Lesley's suggestion that the Coal Measures attained 

 to much greater thickness in the anthracite region than in the 

 bituminous areas hardly accords with the facts as now known, 

 many of them published since he offered his suggestions. It is 

 altogether certain now that the lower three divisions of the Coal 

 Measures in Pennsylvania, the Pottsville, the Lower Coal Group 

 and the Lower Barren Group, do not show any variations which 

 would justify one in basing a theory upon them ; and it is much 

 more than probable that the Upper Coal Group and the Permo- 

 Carboniferous attain their greatest thickness in the north central 

 portion of the Appalachian basin, and that they diminish in 

 thickness westwardly, northwardly and eastwardly from south- 

 western Pennsylvania, as abundantly appears from the measure- 

 ments made by I. C. White and by the writer in Pennsylvania, 

 Ohio and West Virginia. In any event, the thickness of the 

 mass in northeastern Pennsylvania was small in comparison with 

 the thickness of the series in Virginia, West Virginia and 

 Kentucky, on the southeastern edge of the Appalachian basin ; 

 yet in those states the coal shows no tendency to be anthracite ; 

 that of the Imboden coal bed of Virginia and Kentucky, almost 

 at the base of the Lower Coal Group of Pennsylvania, is richly 

 bituminous. 



Nor does the theory that anthracite is bituminous coal con- 

 verted by heat due to mechanical force, commend itself in this 

 connection. The crushed and polished coal of the Broad Top 

 field is bituminous, whereas the uncrushed coal of the Northern 

 field in the same strip is anthracite. The Quinnimont coal, in 

 the gently flexed New River district of West Virginia, has 



