6/4 MARIUS R. CAMPBELL 



rearrangement of the drainage in West Virginia. The fact that 

 the extreme head branches of the Atlantic streams have been 

 enabled to cut below the bed of the Chattahoochee seems also 

 to show that these streams have had a decided advantage since 

 the elevation of the Tertiary peneplain to its present altitude. 



(4) REMOTE CHANGES SHOWN IN THE STREAMS OF THE APPALA- 

 CHIAN VALLEY. 



So far we have considered only those cases in which geologic 

 structure has played little or no part in shaping the courses of 

 the streams. While in such cases the effect of surface tilting is 

 most pronounced, it has also operated in the Appalachian Valley 

 where geologic structure dominates the whole topography. 



No one can consider for a moment the drainage basins of the 

 Susquehanna, Potomac, James, and Roanoke rivers without being 

 impressed by their unsymmetrical condition. In the case of the 

 Roanoke and New rivers, there can be no doubt that the former 

 is encroaching upon the grounds of the latter. This is so appar- 

 ent that a traveler on the railway easily distinguishes the differ- 

 ence in grade on the two sides of the waterparting between them. 

 In this case, although the divide may now be migrating toward 

 New River, it is very certain that this has not continued for a 

 long time, else New River would have been captured long ago. 

 Here we are not concerned about the migration of the divide, 

 but rather about its non-migration. Since for a long time, New 

 River must have been working at a great disadvantage against 

 Roanoke River, why has not the latter cut through the divide at 

 Christiansburg and captured the entire head of the former stream? 



As has been explained, the preservation of a divide under 

 unfavorable circumstances is no more anomalous than the migra- 

 tion of a divide toward the axis of uplift ; it simply indicates 

 that the unfavorably located stream has been assisted in the 

 preservation of its drainage basin by an uplift which corre- 

 sponded with the preexisting divide between the contending 

 streams ; and which by its continued movement has prevented 

 the aggressive stream from absorbing its weaker neighbor. 



