246 National Geograjphic Magazi/txe. 



hardly to be thought that the location of the Juniata in the 

 Narrows below Lewistown between Blue Ridge and Shade moun- 

 tain and its avoidance of Tuscarora mountain could have been 

 defined at that early date. But all these Medina anticlines rise 

 more or less above the Cretaceous baselevel, and must have had 

 some effect on the position taken by the river about the middle 

 of that cycle when its channel sank upon them. Blue Ridge and 

 Black Log anticlines rise highest. The first location of the cross- 

 country stream that led the early Juniata away from its initial 

 syncline probably traversed the Blue Ridge and Black Log anti- 

 clines while they were yet buried ; but its channel-cutting was 

 much retarded on encountering them, and some branch stream 

 working around from the lower side of the obstructions may have 

 diverted the river to an easier path. The only path of the kind 

 is the narrow one between the overlapping anticlines of Blue 

 Ridge and Shade mountains, and there the Juniata now flows. 

 If another elevation should occur in the future, it might happen 

 that the slow deepening of the channel in the hard Medina beds 

 which now floor the Narrows would allow Middle creek of Snyder 

 county to tap the Juniata at Lewistown and lead it by direct 

 course past Middleburgh to the Susquehanna ; thus it would 

 return to the path of its youth. 



The location of the Juniata at the end of Tuscarora mountain 

 is again so definite that it can hardly be referred to a time when 

 the mountain had not been revealed. The most likely position of 

 the original cross-country stream which brought the Juniata into 

 the Wiconisco syncline was somewhere on the line of the existing 

 mountain, and assuming it to have been there, we must question 

 how it has been displaced. The process seems to have been of 

 the same kind as that just given ; the retardation of channel- 

 cutting in the late Cretaceous cycle, when the Medina beds of 

 Tuscarora anticline were discovered, allowed a branch from the 

 lower part of the river to work around the end of the mountain 

 and lead the river out that way. The occurrence of a shallow 

 depression across the summit of the otherwise remarkably even 

 crest of Tuscarora mountain suggests that this diversion was not 

 finally accomplished until shortly after the Tertiary elevation of 

 the country ; but at whatever date the adjustment occurred, it is 

 natural that it should pass around the eastern end of the mountain 

 and not ai'ound the western end, where the course would have 

 been much longer, and therefore not successfully to be taken by 

 a diverting stream. 



