GEOGRAPHICAL CHANGES DURING PENNSYLVANIAN 145 



others of shale and sandstone. He states also that fragments increase in 

 size eastwardly, there being at the east end many 5 to 6 inches in diam- 

 eter. These large pieces, as well as those of shale and sandstone, could 

 not have been transported far. Mr Lyman* calls attention to the 

 rapidity with which the fragments decrease in size northwardly as evi- 

 dence of speedy loss in transporting power. Comparisons of tabulated 

 sections given in the Anthracite atlases of the Pennsylvania survey shows 

 that conglomerate areas are separated by areas of finer deposits in which 

 shale is abundant. The conditions are such as would be found in a lake 

 basin filled with confluent delta deposits. 



The eastern border of the West Virginia- Virginia basin is not so 

 apparent. At both the north and the south end the lower beds of the 

 Pocahontas are more or less conglomerate, but midway along the outcrop 

 no conglomerate is seen and even such sandstones as are present are not 

 coarse. But in this basin the deposits quickly lose their coarseness toward 

 the west, and the Pocahontas coal bed itself diminishes in that direction, 

 so that there is much probability in Mr M. E. Campbell's t suggestion 

 that the present outcrop line is not far from the original eastern limit of 

 the basin. 



Elevation at the east and depression on the west side of the great 

 basin became more pronounced after the Pocahontas deposits had been 

 laid down. Great sandstones were spread over the region, all extending 

 farther northward on the east than on the west side, while each in turn 

 overlaps its predecessor and for some distance before disappearance rests 

 on Mississippian beds. The. Rockcastle sandstone was the first to reach 

 the deep valleys of Kentucky and Ohio, and in the latter state it seems 

 to occupy a broad valley along the western margin of the Carboniferous 

 field, extending from Lake Erie southwardly into Kentucky, where it 

 may be that the valleys described by Campbell and Sullivan were its 

 tributaries. In the northern and northwestern parts of the great basin 

 the subsidence was nearly uniform, there being but slight valuations in the 

 section; but from Kentucky southward there was clearly a constant in- 

 crease along the easterly side into Alabama, where throughout the sub- 

 sidence was very great, the Eockcastte deposits being several times as 

 thick in Alabama as along the western escarpment of the Tennessee 

 plateau. Yet this subsidence was not without irregularities and local 

 foldings, for intervals between the great sandstones show at times re- 

 markable variation. There were long periods of comparative quiet, 



* B. S. Lyman : Original southern limit of the Pennsylvania anthracite beds. Trans. 

 Am. Inst, Min. Eng., 1902. 



t Cited by D. White In Bull. Geol. Soc. Am., vol 15, p. 276. 



