Campbell — Changes in the Drainage of Virginia. 25 



feet deep which it has carved in the calcareous strata of the 

 Cambrian and Lower Silurian. Its larger tributaries have 

 nearly kept pace with the river in the corrasion of their chan- 

 nels, but the smaller ones have only succeeded in cutting 

 narrow Y-shaped gorges through which they discharge their 

 waters into the main stream. The Holston, a larger stream, 

 flowing parallel to the Clinch and 20 miles southeast of it, has 

 only cut from 50 to 100 feet below its ancient valley. 



This shows greater elevation of the Clinch drainage basin or 

 a differential uplift with its maximum development in the 

 region northwest of Clinch river, sloping gradually southeast 

 to a minimum in the valley of the Holston. While this up- 

 lift was purely orogenic in character, it must not be supposed 

 that it formed steep slopes in both directions away from the 

 axis of the fold, but rather that it raised the surface in a low 

 broad ridge along a certain axial line which can be located 

 only in the most general way. Judging from evidence ob- 

 tained in a more extensive study of the field, this axis passes 

 north of Norton but at what distance it is difficult to determine. 

 Along the crest of the fold there was probably a broad belt 

 where but little tilting occurred which accounts for the unaf- 

 fected condition of the northern tributaries of Powell and 

 Guest rivers.* The surface southeast of this axial line being 

 thus tilted, those branches flowing southeast to the Clinch 

 river would be accelerated, while the headwaters of Powell 

 river would be retarded since they flow toward the axis of 

 uplift. Clinch river having a greater volume of water than 

 Powell river would more rapidly deepen its channel even 

 though it had to contend against the upturned conglomerate. 

 The branch A, fig. 2, flowing on the soft shales above the 

 conglomerate, easily cut back along the strike and diverted the 

 head branches of Powell river; first the small one B from 

 the southeast was conquered which pushed the divide to 

 Coeburn ; Tom creek was captured at this point and the 

 process of robbing was greatly accelerated by the increased 

 volume of water derived from that stream ; as time pro- 

 gressed, the conquest extended westward until at last it re- 

 versed the entire drainage east of Norton. This robbing 

 could be easily extended so as to include Benges branch which 

 comes out of the mountain upon almost the summit of the 

 divide and flows west to Powell river. Should Guest river 

 lower the divide but 20 feet this branch would flow to the 

 eastward, but this change is not likely to occur since Powell 

 river is much more actively at work on this divide than Guest 



* A fuller discussion of this evidence is given in the Geomorphology of the 

 Southern Appalachians by C. Willard Hayes and Marius R. Campbell. Nat. 

 Geog. Mag., vol. vi. 



