CORRELATION 20 



Q 



ening of the Lower Pottsville, which attains fully 175 feet in some places 

 and clearly has a new member in the lower portion ; but in Ohio the 

 western border lies for the most part far east from the old shore line, so 

 that for some distance there is simply the northwest Pennsylvania sec- 

 tion, with the Sharon sandstone somewhat irregular in occurrence. 



As one approaches Jackson county, in southern Ohio, where the beds 

 extend westward farther than in the northern part of the state, lower 

 members of the Pottsville reappear, and one recognizes there the two 

 members of the Sharon, with the Jackson Shaft coal bed between them. 

 No further change appears until one has passed, in Kentucky, to 40 or 

 50 miles south from the Ohio river, where there is a mass of shales 

 underlying the lowest Ohio bed. Thence southward the change is very 

 marked, so that in Tennessee one finds appearing below these shales the 

 Bonair and Etna sandstones, which persist to the last exposures in Ala- 

 bama, with a varying thickness of beds below them, to the Lower Car- 

 boniferous. Meanwhile a change takes place in the Upper Pottsville. 

 Until one has gone southward 40 or 50 miles into Kentucky, the section 

 shows little variation except in the loss of its limestones, but there the 

 column quickly expands throughout, so that in southern Kentucky and 

 northern Tennessee the conditions are as on the eastern border. In 

 much of Tennessee, as well as in northern Alabama, the Upper Potts- 

 ville has been removed by erosion, but it reappears in the Warrior, 

 Coosa, and Cahaba fields of Alabama, evidently greatly expanded and 

 bearing little resemblance to any sections obtained in northern Tennessee. 



Within the basin, beginning at the north, one finds the Lower Potts- 

 ville, represented by the Sharon sandstone, disappearing quickly toward 

 the south, not to reappear until one has gone some distance into West 

 Virginia. The great thickness assigned to the Pottsville in Clearfield 

 county is to be explained by the absence of the Shenango shales and 

 lower beds, so that the Pottsville and Logan are continuous. There is 

 good reason for believing that there one has only the upper members of 

 the section. In the preceding pages Mr W. G. Piatt's Red Bank section 

 in Armstrong county has been referred to the Pottsville in deference to 

 the opinion of one for whose acumen the writer has great respect ; but 

 the conditions observed farther south and southeast in Indiana and 

 Westmoreland counties seem to forbid this reference, and to support 

 Mr Piatt's contention that the limestone is not Mercer, but rather the 

 Silicious (Tuscumbia) of the Lower Carboniferous, and that the great 

 underlying sandstone is Pocono (Logan). The writer is convinced that 

 there the Pottsville is represented only by its highest members, the 

 Homewood and upper Mercer, the lower members of the Pottsville hav- 

 ing thinned out eastwardly and southeastwardly. 



