670 MARIUS R. CAMPBELL 



the tilting exerted its full force in producing a rearrangement of 

 the drainage lines. The result of this exposed condition is that 

 most of the streams have been captured by branches working 

 back from the northwest producing the imbricated arrangement 

 shown in Fig. 1 1. 



In the light of the previous discussion, there seems to be no 

 question that this condition is due to a gentle tilting of the sur- 

 face toward the northwest from near the Greenbrier River. In 

 this region the inter-stream areas are of such an elevation that 

 the principal migration must have occurred long ago — when the 

 general surface was many hundreds of feet higher than today, 

 and at a time when the surface relief was slight. There were 

 probably two periods when such a change could have taken 

 place, contemporaneously with the completion of either the Cre- 

 taceous or the Tertiary peneplains. The character of the changes 

 point rather to the latter than to the former; for if the tilting 

 had occurred in Cretaceous time, subsequent changes would, in 

 all probability, have obliterated the courses of the minor streams. 

 But it is the minor drainage lines which are here the character- 

 istic features and which were probably formed long after the 

 uplifting of the Cretaceous plan from baselevel. 



{b~) Big Sandy and Clinch River basins. — Southwest of New 

 River, the streams flowing directly to the Ohio are encroaching 

 upon the streams of the Tennessee system, although the latter 

 has a decided advantage in the soft limestones and shales of the 

 Appalachian Valley. Tug fork of Big Sandy River has cut 

 entirely across the coal field, and its head is within a mile of 

 Clinch River at a point fifteen miles below the source of the lat- 

 ter.' Not only has it encroached to within such a short distance, 

 but it is flowing more than 300 feet below Clinch River at the 

 point of its nearest approach. In its backward cutting it has 

 reached the Valley limestone and, if conditions remain unchanged, 

 it will be but a short time, geologically speaking, until it will 

 capture Clinch River at this point. The migration of this divide 

 is in the same direction as the cases already cited and is evi- 



^ See the Tazewell Atlas sheet of the U. S. Geological Survey. 



