■913.] ORTMANN— THE ALLEGIIENIAN DIVIDE. 347 



occupies only the valley, and very little of the mountains, while every 

 succeeding one cuts farther back into the mountains (Campbell, 

 1896, p. 675). 



In the region of the uppermost Roanoke there is a good instance 

 of more recent stream piracy. The headwaters of the North Fork 

 are running first in a southwesterly direction in a valley, which is 

 clearly continued toward New River; but just north of Christians- 

 burg this fork makes a sharp bend, cuts through Paris Mountain, 

 and flows then eastward and northeastward. It is clear that the 

 Roanoke has captured here a former tributary of New River (see 

 Campbell, 1896, p. 674, and our map, PI. XII., and profile pi. XIV, 

 fig. I). 



James River has cut much farther into the Allegheny Mountains. 

 It is doubtful whether the original streams in this region belonged 

 to New River. According to Hayes and Campbell (1894, p. no) 

 no important shifting of divides has taken place in this region during 

 the Tertiary cycle, although, as we have seen, Campbell (1896) 

 assumes stream piracy between James and Roanoke. This region 

 is extremely complex in structure and has little been investigated. 



Coming to the Potomac drainage, we observe that this river has 

 cut clear across the mountains, and has reached, in northeastern West 

 Virginia and in western Maryland, the western boundary of the 

 Allegheny Plateau, Allegheny Front, and at one point has even cut 

 through this and encroached upon the Allegheny Plateau, draining 

 now a longitudinal synclinal valley. (See our map, PI. XII., and 

 profile pl. XIV, fig. 2.) As to the former drainage in this region very 

 little is known. But according to Campbell (see above) the Potomac 

 has robbed, in the region of the mountains, James River, and in one 

 case, in the Shenandoah Valley, we have instances of more recent 

 stream piracy during the Tertiary cycle. The Shenandoah is a 

 rather recent stream, which has captured in succession several older 

 streams, running originally independently through Blue Ridge east- 

 ward (see Davis, 1891, p. 576, and Abbe, 1889, p. 68). 



The Susquehanna in Pennsylvania has progressed farthest in the 

 capture of western streams. It has not only cut clear across the 

 mountains, but also has invaded a large section of the plateau, which 



