522 PROCEEDINGS OF THILADELPHIA MEETING. 



represented which were produced at different periods and successively elevated 

 with little wai-ping. 



Features of the Tennessee Basin 



PENEPLAIN GROUPS 



Inspection of the Tennessee basin in the Great valley reveals well developed 

 penei)lains at four altitudes. The ui)[)eruiost series appears in penephiins and 

 plateaus near the heads of the main streams from 3,o00 to 3,700 feet high, falling 

 slightly away from the divides. As the streams increase in size these phiins are 

 more and more dissected by sharp gorges of later origin, until along the northwest 

 front of the Unakas only the most insoluble rocks approximate the original height 

 at 3,000 to 3,200 feet. In the valley of Tennessee some ridges of hard rock remain 

 at this height, but are considerably dissected. On Cumberland plateau northwest 

 of Knoxville a large area of knobs and level ridges on one of the main divides 

 remains at 3,100 to 3,200 feet. As the draining streams grow larger this ancient 

 plain is dissected and supplanted by another and lower plain. 



This second great grou[) of forms is found at altitudes of 2,000 to 2,600 feet. It 

 begins as a series of peneplains along the upper Holston at 2,300 to 2,500 feet. 

 Beliind the barrier of the Unakas the tributaries of the Tennessee, the Xolichucky, 

 Frencii Broad and Pigeon rivers, have cut out broad pene])lains from 2,300 to 2,700 

 feet. These are very well preserved, and in every case the}' sIuav a slight but steady 

 rise upstream, whatever the direction of flow. As before statetl. the Pigeon pene- 

 plain is uniforml}' higher than the ailjacent French Broad plain. Passing down 

 the Great valley the second peneplain is much dissected, and appears only in sand- 

 stone ridges in the valley or in peue])lain remnants along the foothills of the Unaka 

 mountains at elevations ranging from 2,100 to 2,400 feet. Tlie Clinch and Bays 

 mountains and the Cumberland front, esi)ecially the former, are fine examples of 

 baseleveled ridges. In the lower Tennessee valley all tiaces of this peneplain have 

 been removed. 



The third group of surface forms attains i)roiuinence in the Tennessee valley 

 after the confluence of Watauga river an<l the noi-th and south forks of Holston 

 river at altitndes of 1,()00 to 1,800 feet. Above the junction it is only manifest in 

 broad flood-j)lains, bottoms and similar features lingering between the remnants 

 of the peneplain last described. For oOor (50 miles southwest down the valley this 

 altitude of 1,H00 to 1,(S00 feet is prominent in l)road peneplains. These become 

 more and more dissected, until only scattered ridges attain that height, and the 

 country stands at 1,000 to 1,100 feet. Along either side of the Great valley many 

 remnants of this peneplain appear ; on the Iliawassee drainage through the Unakas 

 it is finely developed at 1,700 to 1,S00 feet, and on the opposite side of the valley 

 AValdens ridge and Cuni1)erland plateau exhibit broad areas at 1,500 to 1,700 feet. 



The last series appearing in the Tennessee valley becomes predominant after the 

 union of Xolichucky, French Broad and llolston rivers above Knoxville. Broad 

 bottoms and gravel-covered terraces and valleys mark the emergence of the rivers 

 at 1,000 feet, their courses between that altitude and 1,()00 to 1,800 feet being largely 

 confined to narrow valleys and gorges. Below these points broad valleys appear, 

 widen out into peneplains and soon occupy the entire valley at 1,000 to 1,100 feet, 

 extending southwestward at that height for many scores of miles. In the course 

 of still more recent ero.sionthe streams have carved narrow canvons, which slowlv 



