146 J. J. STEVENSON CARBONIFEROUS OF APPALACHIAN BASIN 



during which coal beds of great extent and great economic importance 

 were formed. • • 



The ocean found ingress at few localities and apparently for only 

 brief periods. Professor Saiford * discovered a limestone in Grundy 

 county of Tennessee within the Bonair and very near the extreme western 

 outcrop. This, as he states, a rare occurrence in Tennessee, contains a 

 marine fauna, evidently marking the head of a bay communicating with 

 the interior sea. Mr M. E. Campbell reports a fossiliferous shale not 

 far above the Etna horizon in McDowell county of West Virginia, 300 

 miles northeast from Professor SafEord's locality and only about 15 miles 

 from the extreme eastern outcrop; and Mr David White has observed 

 marine forms very near the same horizon on JSTew river, east from Sewell. 

 This may mark the head of a bay opening to the Atlantic. No marine 

 fossils have been observed anywhere in the intervening space. In central 

 Alabama, Mr McCalley found several beds with marine fauna in the 

 higher part of the column, but no observer has recorded the presence of 

 marine forms in either Georgia or eastern Alabama. 



The post-Pocahontas sandstones of the Eockcastle give a clue to the 

 land boundaries. In ascending order they are the Etna, Bonair, Eock- 

 castle, and Sharon. All are conglomerate to coarse, more or less pebbly 

 sandstones at most localities along the easterly border. Followed west- 

 wardly in Alabama, the Etna becomes a not very coarse sandstone and 

 the Bonair shows only occasional pebbles; but beyond the central part of 

 the state both beds thicken toward the western border, indicating that 

 the land area, so distinct on the east and south, must have extended 

 northwardly on the west side through Mississippi almost to the Tennessee 

 line. There, however, one is beyond the strict limits of the Appalachian 

 basin and is in line with the Indiana-Illinois area, cut off abruptly by 

 erosion in Kentucky 200 miles north from the Alabama exposures. At 

 the extreme western outlier in Tennessee these two sandstones are cross- 

 bedded and not coarse, and the Etna retains these characteristics at most 

 localities in central and western portions of the Tennessee coal field; 

 but the Bonair is usually more or less conglomerate and is very coarse 

 near its termination, in the northern portion of the state. 



The Eockcastle and Sharon sandstones cannot be recognized in central 

 Alabama ; there is good reason to suppose that the higher bed is no longer 

 present, having been removed by erosion. But sandstones and conglomer- 

 ates are so numerous and so considerable in the upper part of the column 

 as to leave no room for doubt respecting continuing elevation of the inclos- 

 ing area east, west, and south. In much of the central and western part of 



• J. M. Safford : Geology of Tennessee, p. 367. 



