48 MEMOIRS NATIONAL ACADEMY OF SCIENCES. [vol.xii. 



nent. The general parallel or axial courses of the strata within the valley favored the develop- 

 ment of a corrugated topography, and the streams located upon soft rocks eroded deeply and 

 rapidly and tended to migrate from the harder to the softer and lower rock surfaces. This 

 lateral movement was supplemented by the southwestward slope of the general land surface, 

 which favored longitudinal movement; and migration was possibly even further favored by the 

 location of the various local axes. The erosion of land surface and the growth of the newly 

 forming peneplain thus spread from the softer rocks up the slopes toward the axes and the old 

 reinforced divides; and the general southwestward slope of the surface favored the encroach- 

 ment and extension of the peneplain toward the northeast, in the general direction of the present 

 Appalachian Valley, and of course erosion was relatively more rapid near the larger streams. 

 Such relations, in outline, indicate the general dynamic tendencies of this newly forming pene- 

 plain and also indicate in what general direction drainage development was likely to take place. 



At this critical period in the history of the Tennessee drakiage, the period of transition 

 from the Cretaceous to the Tertiary peneplains, detailed studies are unfortunately very few in 

 mmaber. For this reason, probable, provisional, and suggestive relations must form a promi- 

 nent featm'e in the discussion which foUows. 



Early in the Tertiary an uplift occurred along the axis P, plate 57, C, according to Hayes 

 and Campbell ('94, p. 92), reaching its maximum at Chattanooga and declining gradually to the 

 north. This axis may be expected to have had a fundamental influence upon the embayment 

 streams and the transverse drainage in general, particularly the Cumberland system. Consider- 

 ing the resistant sandstones over which the transverse drainage flowed to the west, even a 

 moderate uplift along this axis would increase the imfavorable conditions for such streams. 

 This uplift in itself may have destroyed the lower Cumberland-Emory River water gap, and 

 possibly the distance of Cumberland Gap from it permitted its existence for a longer time. The 

 diversion of water from these gaps to the lower Tennessee system would help make it possible 

 for the Tennessee to maintain its course across Walden Ridge. Not only would this axis favor 

 early diversion of the Cumberland drainage, but the general slope of the land sin"f ace and the 

 development of the axial streams upon softer rocks would tend to begin at the southwestern 

 margin and migrate up the Great Valley slope. Furthermore, it is probable that even if the 

 uplift was general and not localized, the relatively softer rocks of the Appalachian Valley tract 

 would erode faster than the bordering areas of more resistant rocks. All of these conditions 

 combine to favor the idea of an early southward diversion of the Emory drainage; and because 

 of the great volume of the former stream enough erosion had perhaps been done to be a deter- 

 mining factor in the location of the present Emory River. 



This southward diversion was accomplished by the northward migration of a stream north 

 of the mouth of the Hiwassee River. The Little Tennessee was thus diverted to the southward, 

 and with the continued migraton of streams progressively to the northeast the drainage of the 

 region west of Clinch Mountain was diverted by the Lower Clinch below Lone Moimtain (at 

 about Walkers Ford). 



At this time it is probable that the upper Holston, flowing through Big Moccasin Gap (plate 

 59) was a tributary of the Clinch and aided that stream in maintaining a part of its ancient 

 course on the Cretaceous peneplain, as it was elevated and was able to cut through Lone Moun- 

 tain, which arose in its path. As Clinch Valley was degraded, a tributary of Clinch River was 

 able to capture and divert the upper Powell River and thus make the last important capture 

 from the Cumberland system. 



In a similar manner the upper French Broad was probably diverted at an early date by the 

 upper part of the Tennessee proper and by the lower French Broad. The Nolichucky was 

 probably not tributary to the French Broad at this time, but was a part of the lower Holston. 

 Several terraces found by Glenn ('11, p. 44) at Aliens Bridge on the lower Nolichucky "on 

 the general country levels," 220 feet above the present flood plain, shows that this part of the 

 stream has long flowed in its present channel. The progressive northeastward migration of 

 tbis plane of degradation moved up the Great Valley to the vicinity of Big Moccasin Gap. At 

 the forks of the Holston, a few mUes farther downstream, this peneplain is clearly recognized by 



