232 National Geographic Magazine. 



divide would be important. For this reason, it might be carried 

 from the Newark belt as far as the present Alleghany front, 

 beyond which further pushing would be slow, on account of the 

 broad stretch of country there covered by hard horizontal beds. 



The end of this is that, under any of the circumstances here 

 detailed, there would be early in the Jurassic-Cretaceous cycle a 

 distinct tendency to a westward migration of the Atlantic-Ohio 

 divide ; it is the consequences of this that have now to be 

 examined. 



32. Capture of the Anthracite headwaters by the growing Sus- 

 quehanna. — Throughout the Perm-Triassic period of denudation, 

 a great work was done in wearing down the original Alleghanies. 

 Anticlines of hard sandstone were breached, and broad lowlands 

 were opened on the softer rocks beneath. Little semblance of 

 the early constructional topography remained when the period of 

 Newark depression was brought to a close ; and all the while the 

 headwater streams of the region were gnawing at the divides^ 

 seeking to develop the most perfect arrangement of waterways. 

 Several adjustments have taken place, and the larger streams 

 have been reversed in the direction of their flow ; but a more 

 serious problem is found in the disappearance of the original 

 master stream, the great Anthracite river, which must have at 

 first led away the water from all the lateral synclinal streams. 

 Being a large riyer, it could not have been easily diverted from 

 its course, unless it was greatly retarded in cutting down its 

 channel by the presence of many beds of hard rocks on its way. 

 The following considerations may perhaps throw some light on 

 this obscure point. 



It may be assumed that the whole group of mountains formed 

 by the Permian deformation had been reduced to a moderate 

 relief when the Newark deposition was stopped by the Jurassic 

 elevation. The harder ribs of rock doubtless remained as ridges 

 projecting above the intervening lowlands, but the strength of 

 relief that had been given by the constructional forces had 

 been lost. The general distribution of residual elevations then 

 remaining unsubdued is indicated in fig. 25, in which the 

 Crystalline, the Medina, and the two Carboniferous sandstone 

 ridges are denoted by appropriate symbols. In restoring this 

 phase of the surface form, when the country stood lower than 

 now, I have reduced the anticlines from their present outlines 

 and increased the synclines, the change of area being made 



