1887.1 -•- ' ^ [Stevenson. 



Great planes of erosion are shown in all parts of the "Valley" from 

 the Tennessee line to the eastern side of Montgomery county ; no doubt 

 they are continuous thence into Pennsylvania, -where such planes are 

 sufficiently distinct. At all localities they illustrate effects of erosion 

 during a long period in which the channel-ways of the main streams are 

 not deepening materially. 



By some means the erosive or channel-deepening power of the New 

 river has been greatly increased since the erosion of the upper planes was 

 completed ; for the river has excavated a trorge 255 to 300 feet deep with 

 the hills abrupt on one or both sides for considerable distances ; while ero- 

 sion extends at best to but a little way from the river. The tributary 

 streams flow for the most part in comparatively narrow valleys, even 

 where the conditions appear to be such as to favor extended erosion. 

 Meanwhile the destruction of the elevated planes has gone on irregularly ; 

 the upper bench south from Walker mountain has suffered little in Mont- 

 gomery county except near the river. But that in Giles county has been 

 eaten away and another, widely extended, has been formed at a lower 

 horizon ; and there appears to be nothing south from Walker mountain to 

 compare in extent with the lower plain north from that mountain. 



While the erosion of the "Great Valley" and of the region drained by 

 New river appears easily referable to a simple plan, the conditions in the 

 limestone area of Tazewell, Russell and Scott counties, drained by Clinch 

 river, are not so clear. Benches exist, but they are not so obvious as are 

 those in the valley, they do not always carry a deposit loaded with peb- 

 bles and they seem rarely to have great extent. One gravel deposit was 

 found on the line between Russell and Scott within a mile of Clinch river 

 and at G40 feet above that river at Osborn's ford, making its height above 

 tide not far from 1920 feet. The pebbles are rarely larger than a hen's 

 egg, and are mostly quartz ; comparatively few could have been derived 

 from the region now drained by the Clinch, and most of them must have 

 come from the Blue Ridge or further at the south. 



The Clinch and North llolston are as handsomely terraced as the New 

 river and its tributaries. The " bottom" of Clinch river appears to main- 

 tain a uniform height of about fifteen feet above low water ; a fine terrace 

 is shown near Osborn's ford at ninety-five feet above the river or 1375 feet 

 above tide, and it is present on both sides of the river at a little way above 

 the ford. A higher bench is shown on the southerly side, but its height 

 could not be ascertained. Near Nash's ford in Russell county, three ter 

 races are crossed as one descends to Clinch from the south. These are 

 about 155, 40 and 15 feet above low water at the ford. The highest 

 reaches far back from the river and its height above tide is not far from 

 1700 feet. A fine terrace was seen on the north fork of Holston below 

 the mouth of Laurel creek in Smyth county, where the top of the deposit 

 is between eighty-five and ninety feet above the river or at not far from 

 1625 feet above tide. The deposit on these river terraces consists of sand 

 and clay carrying abundance of boulder, all apparently of local origin. 



