424 STEVENSON— THE FORMATION OF COAL BEDS, [^'ov. i, 



all intents and purposes the same in all regions and in all periods, 

 from the Devonian coals of Bear Island in the Arctic to the Tertiary 

 coals of Wyoming or Trinidad; but the varying descriptions and 

 explanations presented by students make equally certain that one 

 cannot ascertain what the essential conditions are, if his investiga- 

 tion be confined to areas embracing a score or even several hundreds 

 of square miles. The investigation must cover a great area, in 

 which merely local features do not obscure those which are general 

 and which actually bear upon the problem in hand. Such an area is 

 the Appalachian Basin of the eastern United States, where one 

 finds the Pennsylvanian or Coal Measures divided into 



Dunkard Greene 



Wheeling Washington 



Monongahela 



Athens Conemaugh 



Allegheny 



Pottsville Beaver 



New River 

 Pocahontas 

 The order is descending.^ 



The Appalachian coal field, now embracing approximately 

 70,000 square miles of almost continuous deposits, occupies only a 

 part of the original area. The deep synclinal basins of anthracite 

 in eastern Pennsylvania are separated by 50 to 100 miles from the 

 great bituminous region at the west, while southwardly one finds 

 insignificant fragments along the eastern side until he comes to 

 Georgia and Alabama. The greatest extent of the area of deposit 

 was probably at the close of the Pottsville, when it reached from 

 southern New York in west southwest direction to beyond central 

 Alabama, more than 800 miles; at the north, it spread from the 

 old Appalachian land, at the east, westward to beyond Newark in 



-J. J. Stevenson, "Carboniferous of the Appalachian Basin," Bull. Geo!. 

 Soc. Anier., Vol. 18, 1907, p. 178. The Pottsville is subdivided in this paper 

 into Beaver and Rockcastle. I. C. White, in West Virginia Geol. Survey, 

 Vol. la, 1908, p. 13, has suggested that Rockcastle be replaced by New River 

 and ' Pocahontas ; this should be accepted, as Stevenson did not assign 

 proper significance to Pocahontas, regarding it as merely a subordinate stage. 



