610 A. W. GRABATJ TYPES OF SEDIMENTARY OVERLAP 



occur. Upward it passes into sandy shale and argillaceous sandstone. 

 The thickness averages 350 feet, and it is succeeded by the Newman 

 limestone, 100 to 250 feet thick, and the Pennington shale, which is 

 occasionally absent. Above this is a great erosion break, followed by 

 Pennsylvanian sandstone. The shale above the Black shale is referred 

 to the Waverly, of which it probably constitutes the upper portion only. 

 As at Irvine, the transition from the Black shale to the overlying beds 

 is probably a gradual one. 



Taken together with the section at Chilhowee mountain, Tennessee, 

 where the Grainger shale, 1,100 feet thick, separates the Black shale 

 from the Newman limestone — and with the section in Walden ridge, 

 30 miles northwest, where the Newman limestone rests directly on the 

 Black shale — it becomes apparent that a ridge of land extended south- 

 eastward, approximately along what is now the Walden ridge of Ten- 





Figure 5. — Diagram of Cumberland Ridge showing Relationship of interior Sea to oceanic 



Channel. 



nessee and the Cumberland mountains and westward in Kentucky, separat- 

 ing the interior basin from a channel to the east of this ridge. Whether 

 this channel was in direct communication with the Atlantic to the south 

 or whether it represented an encroaching arm of the sea from the north 

 is a matter for further investigation. The sections given so far indicate 

 that the latter condition obtained, since the formations overlap pro- 

 gressively southward along this channel. West of this barrier the Missis- 

 sippian sea was slowly encroaching southward and eastward, as shown 

 by the overlapping beds, until in Saint Louis time the barrier became 

 submerged and the Newman limestone was spread uniformly over the 

 whole area. The relationship of the interior sea to this channel and 

 to the formations accumulating in each is shown in the accompanying 

 diagram. 



In the region about Eome, Georgia,* the Frog Mountain sandstone 

 rests unconformably on the Eockmart and other formations in the south- 

 west area and in the adjoining Fort Payne quadrangle. "It consists chiefly 

 of white quartzitic sandstone and yellow porous sandstone, the latter prob- 



* Rome folio. 



