The Rivers and Yalleys of Pennsylvania. 289 



But this master stream deserted its original course on the trans- 

 verse axis of depression because a lateral course across lowlands 

 on softer beds was opened by its side streams ; and in the contest 

 on these lowlands with an external stream, the Susquehanna, the 

 upper portion of the Anthracite was diverted from the hard rocks 

 that had appeared on the transverse axis. The distance of 

 diversion from the axial to the lateral course in this case was 

 great because of the gentle quality of the transverse folding ; or, 

 better said, because of the gentle dips of the axes of the longi- 

 tudinal folds. This appearance of systematic re-arrangement in 

 the several riVer courses where none was expected is to my mind 

 a strong argument in favor of the originally consequent location 

 of the rivers and their later mutual adjustment. It may perhaps 

 be conceived that antecedent streams might imitate one another 

 roughly in the attitude that they prophetically chose with regard 

 to folds subsequently formed, but no reason has been suggested 

 for the imitation being carried to so remarkable and definite a 

 degree as that here outlined. 



35. Superimposition of the Susquehanna on ttoo synclinal 

 ridges. — There is however one apparentlj'" venturesome postulate 

 that may have been already noted as such by the reader ; unless 

 it can be reasonably accounted for and shown to be a natural 

 result of the long sequence of changes here considered, it will 

 seriously militate against the validity of the whole argument. 

 The present course of the middle Susquehanna leads it through 

 the apical curves of two Pocono synclinal ridges, which were 

 disregarded in the statement given above. It was then assumed 

 that the embryonic Susquehanna gained possession of the Siluro- 

 Devonian lowland drainage by gnawing out a course to the west 

 of these synclinal points ; for it is not to be thought of that any 

 conquest of the headwaters of the Anthracite river could have 

 been made by the Susquehanna if it had had to gnaw out the 

 existing four traverses of the Pocono sandstones before securing 

 the drainage of the lowlands above them. The backward pro- 

 gress of the Susquehanna could not in that case have been neai'ly 

 fast enough to i-each the Anthracite before the latter had sunk 

 its channel to a safe depth. It is therefore important to justify 

 the assumption as to the more westerly location of the embryonic 

 Susquehanna ; and afterwards, to explain how it should have 

 since then been transferred to its present course. A short cut 

 through all this round-about method is open to those who adopt 



