SOME STAGES OP APPALACHIAN EROSION. 523 



open oat downstream and are bordered by terraces and bottoms from 600 to 700 

 feet above sea. 



Thus in the Tennessee valley are seen four distinct groups of peneplains and 

 associated features, marking four periods of stable land and long degradation. The 

 greatest of these is the first, because it extended to the headwaters of the main 

 rivers, and only the most obdurate and remote masses escaped reduction. Each 

 successive period was less iini)ortant than the preceding as measured by the results 

 accomplished. The forms of any minor period would have been obliterated, how- 

 ever, by a greater subsequent one, so that the record can only be expected to pre- 

 serve those which were in descending order of magnitude. At the present day the 

 most conspicuous are the 1,600 to 1,800 and the 1,000 to 1, 100-foot peneplains, which 

 occupy much of the Great valley, and, swinging around the south end of the Unaka 

 mountains and the Blue ridge, pass northeast along the heads of the Atlantic basins. 



CLINCH SECTION 



The relations of Clinch mountain, the typical baseleveled ridge of Tennessee, 

 furnish an epitome of the whole basin. Rising abruptly from the 1,000-foot pene- 

 plain and flanked on both sides by ridges of the next peneplain at 1,600 to J, 700 

 feet, its summits stand at 2,100 to 2,200 feet; a few points rise to 2,500 feet and a 

 few wind gaps are cut down to 2,000 feet. This average height of 2,200 feet is 

 maintained for 100 miles northeastward to Moccasin gap, near the state boundary 

 in Virginia, the flanking ridges continuing at uniform heights. Northeast of that 

 gap the mountain rises within three miles to 3,200 feet, and its summits continue 

 at that height for 30 miles to Little Moccasin gap. From this point northeastward 

 the mountain is very irregular in height and loses its identity in a great mass, 

 which is for the most part over 4,000 feet above the sea. In this group of ridges 

 the 1,000-foot peneplain is perfectly obvious ; the same characteristics that are con- 

 ceded to Clinch mountain at 2,200 feet are precisely repeated in the portion stand- 

 ing at 3,200 feet and in the flanking ridges at 1,600 feet. Ttierefore the same rea- 

 soning that identifies a baseleveled ridge at 2,200 feet must recognize the abruptness 

 of' the jum[) from level to level and must identify three baselevel periods instead 

 of one. The linear profiles of the ridges are shown on the accompanying map. 



UNAKA-BLUE RIDGE SECTION 



A profile with similar features but less compact in form is taken along the head- 

 waters of the Tennessee branches between the Blue Ridge and the Unaka moun- 

 tains. It starts with a series of plateaus in Virginia and North Carolina, near the 

 state boundary, at heights of 3,100 to 3,200 feet. These are considerably inter- 

 rupted by the residuals between the Ohio streams and the Tennessee basin, but 

 can readily be traced over into the Tennessee basin at heights of 3,300 to 3,500 

 feet. Into this surface are sunk the fingers of the lower system at 2.600 to 2,700 

 feet. On this part of the section the peneplains are much interrupted by residuals 

 and on the divides between the Watauga-Nolichucky and the Nolichucky-French 

 Broad basins the upper peneplain again appears. The second plain is well shown 

 in the French Broad and Pigeon basins at 2,200 and 2,()00 feet, and again on the 

 Tuckaseegee at 2,300 and the Little Tennessee at 2,200 to 2,100 feet. The Nantahalah 

 has barely produced a plain at the upper level of 3,500 to 3,600 feet, while into the 

 edges of this the two Hiawassee peneplains are cut at 2,100 feet and at 1,800 to 

 1,900 feet, with bottoms and terraces sloping up the streams. These plains with 

 small residuals continue in the Nottely and Toccoa basins, and the lower is carried 



