The Rivers and Valleys of Pennsylvania. 249 



40. Other examples of adjustments. — Other examples of small 

 adjustments are found around the Wyoming basin, fig. 26, 



Fig. 26. 



Originally all these streams ran centripetally down the enclosing 

 slopes, and in such locations they must have cut gullies and 

 breaches in the hard Carboniferous beds and opened low back 

 country on the weaker Devonians. Some of the existing streams 

 still do so, and these are precisely the ones that are not easily 

 reached by divertors. The Susquehanna in its course outside of 

 the basin has sent out branches that have beheaded all the centri- 

 petal streams within reach ; where the same river enters the 

 basin, the centripetal streams have been shortened if not com- 

 pletely beheaded. A branch of the Delaware has captured the 

 heads of some of the streams near the eastern end of the basin. 

 Elsewhere, the centripetal streams still exist of good length. 

 The contrast between the persistence of some of the centripetal 

 streams here and their peripheral diversion around Broad Top is 

 a consequence of the difference of altitude of the old lake bottoms 

 in the two cases. It is not to be doubted that we shall become 

 acquainted with many examples of this kind as our intimacy with 

 rivers increases. 



41. Events of the Quaternary cycle. — The brief quaternary 

 cycle does not offer many examples of the kind that we have 

 considered, and all that are found are of small dimensions. The 

 only capturing stream that need be mentioned has lately been 

 described as a " river pirate ;"* but its conquest is only a Schles- 



* Science, xiii, 1889, 108. 



