96 J. J. STEVENSON LOWER CARBONIFEROUS, APPALACHIAN BASIN 



east, that of the Alleghenies of Virginia, it increases, being 1,250 feet in 

 Pendleton, 1,260 feet in Greenbrier, and 2,500 feet in Summers, the 

 greatest thickness being apparently in the vicinit}' of New river. In the 

 Great valle^^ of Virginia and on the border of the Cumberland plateau, 

 in the southern part of the state, it is about 1,100 feet. Westward it 

 thins rapidly along the w^hole line, and everywhere to the northern 

 border of Tennessee it is shale or sandstone with a little limestone ; but 

 in Tennessee, on both sides of the main area, the shales become thinner, 

 more calcareous, and at length become limestone, so as to be included 

 in the Bangor limestone of Mr Hayes. The upper beds persist as shale 

 much farther than do the lower. 



The outlying areas in Georgia show the limestone of the later Max- 

 ville (?) and Shenango extending far to the southeastward, overlapping 

 the Floyd shales or Oxmoor sandstone of that region ; but at the south 

 it appears to be replaced Avholly b}" sandstone, the Oxmoor there being 

 regarded by the Alabama geologists as representing both Maxville(Hart- 

 selle) and Shenango (Bangor). 



So. toward the close of the Shenango, the water-covered area occupied 

 Pennsylvania, Maryland, Virginia, central Tennessee, northwestern Geor- 

 gia, and northern Alabama west from the Blue Ridge line, but practi- 

 cally none of northwest West Virginia, of Ohio, and in Kentucky less 

 than during the Maxville. The subsidence in Pennsylvania and West 

 Virginia west from the Alleghenies was insignificant and ver}' slow, the 

 main trough of sedimentation lying eastward from the Allegheny region. 

 The subsidence extended southward so as to permit the Shenango to 

 overlap the Maxville in Georgia and Alabama as it does at the north. 

 The character of the sediment north from Tennessee, almost invariably 

 red shale or muddy sandstone, shows a continued depression of the 

 mainland at the east, while the same condition for the south is shown 

 by the overlapping of the earlier members of the series. 



The four subdivisions of the Mississippian — the Logan, the Tuscuinbia, 

 the Maxville, and the Shenango — are characterized by definite bound- 

 aries, due to ]jhysical changes, involving for each the whole basin. 



