1912] STEVENSON— THE FORMATION OF COAL BEDS. 429 



was a land area. Ancient Appalachia at the east towered above the 

 old trough of sedimentation, now become a broad valley with 

 irregular surface, while at the west rose the flat-topped Alleghania, 

 hundreds of feet high at the north and separated from Cincinnatia 

 by the broad, shallow valley of the Ohio basin, which deepened 

 southwardly. The eastern valley and the slope of Appalachia were 

 drained by a river following the westerly side of the valley and 

 finding its outlet at the south in Tennessee, where there still re- 

 mained a considerable body of water. A gradually lengthening 

 stream drained the western valley and found its outlet at the south 

 in the body of water, which was continuous around the southern 

 end of Alleghania. 



The story of the Appalachian basin for the Silurian, Devonian 

 and early Carboniferous is one of local deformations, of differential 

 elevations and depressions, of alternating water and dry land areas, 

 of sea invasions and expulsions or withdrawals. Similar condi- 

 tions continued throughout the Pennsylvanian. The subsidence 

 during the earlier stages was evidently differential, increasing toward 

 the south. As one follows the New River formation along the face 

 of the bituminous area, he finds not merely lower and lower beds 

 but, in Alabama, also a vastly increased thickness in each member 

 of the section, so that the mass, belonging apparently in greatest 

 part to the New River, is greater than the whole column in the 

 anthracite area, though that includes the Pottsville and at least two 

 thirds of the Athens. The condition throughout the Pottsville was 

 that of subsidence and the area of deposit constantly increased 

 toward the west. Along the sides of Alleghania and in the Ohio 

 basin, the New River overlaps the Pocahontas and the Beaver over- 

 laps the New River. The character of deposits in the anthracite 

 region and in Alabama affords ground for belief that, while sub- 

 sidence prevailed within the basin to the end of the Pottsville, there 

 was interrupted elevation in much of Appalachia, causing frequent 

 rejuvenation of the streams and preventing eastward expansion of 

 the area of deposition. During the Athens and later periods, that 

 area seems to have been contracting steadily, first at the south and 

 eventually on all sides until, at the close of the Dunkard, completion 



