1912.] STEVENSON— THE, FORMATION OF COAL BEDS. 431 



cloned, the streams have cut their valleys, hundreds of feet deep, 

 and have lined them with terraces. 



The existence of a land area in Alleghania and the Ohio basin 

 is made clear by the distribution of Pottsville deposits. The 

 Pocahontas formation is present in the southern anthracite field and 

 in the western part of the Western Middle, but it is wanting in the 

 Eastern Middle and the Northern as well as in the bituminous 

 region of Pennsylvania and Ohio. Along the eastern outcrop, it is 

 present in the southern part of West Virginia and the adjacent part 

 of Virginia, but it thins away quickly toward the west and north- 

 west. It has not been recognized southwardly beyond Virginia. 

 The New River is very thick in the southern and in the western 

 part of the Western Middle, but is wanting in the northern anthra- 

 cite field. It is very thick in eastern Alabama within the outlying 

 areas, but it loses thickness quickly toward the west. This part of 

 Alabama is a region of non-conformability throughout. Butts^° has 

 shown that that unconformity is found at close of Cambrian, 

 Ordovician, Silurian and Devonian. There is notable non-con- 

 formity of erosion between Mississippian and Pennsylvanian. The 

 sandstone and shale mass, closing the former in eastern Alabama, 

 was removed from a great space prior to deposit of the Pottsville. 

 In the continuous bituminous region, one finds the upper beds of 

 the New River at about 70 miles south from the Pennsylvania line ; 

 the lower beds appear in succession until in the southern part of 

 the state one finds, in all probability, the whole formation. The 

 formation is wholly wanting in the northern part of the state and 

 in by far the greater part of Pennsylvania. Indeed, there seems 

 to be good reason for doubting the accuracy of identifications along 

 the eastern outcrop in the latter state. In southern West Virginia 

 it is possible to trace the formation across the state by means of 

 exposures and the many records of oil-borings preserved by I. C. 

 White. The lower members disappear in succession westwardly 

 against the face of Alleghania and only the uppermost members 



" C. Butts, "Iron Ores, Fuels, and Fluxes of the Birmingham District, 

 Alabama," U. S. Geol. Surv. Bull., 400, 1910, pp. 14-16. 



