NON-MARINE PROGRESSIVE OVERLAP 



635 



Pennsylvania the overlap was not very great at this time. The next 

 higher division, the Sharon (Sewell), extended into western Ohio and 

 northwestern Pennsylvania, while the higher beds, the post-Sharon, ex- 

 tended still farther. The following diagrams, copied from David White's 

 papers, show these relationships : 



Figures 16 I-III. — Relations of Pocahontas (A), Raleigh-Bon Air (B), Sewell (C), and 

 post-Sharon (D), interpreted as overlapping marine series (according to White). 



White assumes that this transgression was that of a water body trans* 

 gressing northwestward, and he so labels it. At the same time he recognizes 

 the fact that most of the formations are either conglomerates or coarse 

 sands, and that these various elastics rest in most cases directly on marine 

 limestones or shales. He further recognizes erosion in this region preced- 

 ing the advent of the Pottsville sediments. 



The material of the Pottsville beds shows that they were derived from 

 disintegrating crystalline material. Their coarser and more undecom- 

 posed character in the Appalachian region indicates this to have been the 

 source of the material. The utter want in the northwestern region of 

 any area which could have supplied this material makes this conclusion 

 unassailable; for, as has already been stated, the successive beds lie on 

 either marine limestones or shales or on finer non-marine sediments. 

 These must have constituted the shore at successive periods of transgres- 

 sion if a Pottsville sea transgressed northwestward, and they should have 

 constituted the source of the material of the Pottsville beds. Such is not 

 the case, as is well known ; for the pebbles of the conglomerate are quartz 

 pebbles and the sand is composed chiefly of quartz grains. 



We are, then, compelled to consider the crystallines of the Appa- 

 lachians as the source of the material of these beds. These beds, there- 

 fore, overlap away from the source of supply, and hence they can not, by 

 any manner of reasoning, be referred to marine or even lake deposits. 

 To refer them to either is to ignore fundamental principles of deposition; 

 yet all or nearly all writers have thus referred them in the past. 



A significant fact in connection with the recognition of these beds as 

 river deposits is the remarkable rounding of all the pebbles of the conglom- 

 erates. This rounding explains their removal so far from their place of 

 origin, for perfectly round pebbles can be rolled hundreds of miles by 

 streams. It also shows that they have been subject to an enormous 



