432 STEVENSON— THE FORMATION OF COAL BEDS. [Nov. i, 



reach Kentucky. The formation can be followed easily along the 

 eastern outcrop beyond central Tennessee, where the lower portion 

 first crosses Alleghania, and becomes continuous with the deposit 

 in the Ohio basin. There one finds the Bonair sandstone, midway 

 in New River, passing across Alleghania, where it rests on Missis- 

 sippian beds. On the western side in the Ohio basin, the higher 

 New River beds disappear northwardly, each overlapped by its 

 successor, so that beyond the Ohio River one finds only the top- 

 most member occupying a long narrow space, extending almost to 

 the present Lake Erie. At the close of the New River, most of the 

 bituminous region within Pennsylvania and northern West \'ir- 

 ginia was above the area of deposit. During the Beaver that area 

 seems to have increased constantly so that, at the close of the 

 Pottsville, x\lleghania had disappeared and the Homewood sandstone 

 or its equivalent covered the whole basin. The last portion of 

 Alleghania to become buried was in Jefiferson, Clearfield, Indiana. 

 Westmoreland and Fayette counties of Pennsylvania. Differential 

 subsidence continued throughout the Pottsville; even in the Beaver 

 the condition is notable. That formation is 250 to 300 feet thick 

 in western Pennsylvania, but on the Kanawha River in central 

 West Virginia it is fully i.ooo feet, while in southwest Virginia 

 the thickness seems to be even greater. 



The Allegheny shows curious irregularities of thickness within 

 the bituminous area, which are due clearly to local disturbances ; 

 but, leaving that feature out of view, one finds in a general way 

 very little variation, except along the western border, where the 

 section is shortened. The thickness may be taken as approximately 

 250 feet. In the anthracite area, the old trough of sedimentation 

 continued and the great influx of materials from Appalachia gave 

 a thickness several times as great. There, too, one finds anomalous 

 deposition, with abrupt changes in structure of coal beds and re- 

 markable variations in the intervals between them, evidence that 

 there were many and serious local disturbances. 



In the Conemaugh, there is less evidence of local disturbance. 

 The variations are, as it were, regular. Measurements across the 

 bituminous region show rapid thickening eastward to the Ohio 



