1887.] 1'^ [Stevenson. 



The Clinch and Holston unite to form the Tennessee, through which their 

 waters reach the Ohio at Paducah, 



The effects of erosion in Bland county are seen in the removal of lime- 

 stone and shales so as to throw the harder rocks into relief as mountains ; 

 to form narrow valleys in limestones near the present lines of faulting, 

 and to scoop out a basin in Devonian and Upper Silurian shales. Within 

 Giles county. New river llows on Knox (Calciferous) limestone, and the 

 later rocks have been eroded from a considerable space on both sides of 

 the stream. The conditions became approximatelj' the same throughout 

 this area after the removal of the Devonian and Upper Silurian, and good 

 illustrations of certain types of erosion are afforded here as well as further 

 southward along New river. 



Remnants of two planes of erosion, one 225 (1810 feet above tide) feet 

 and the other 115 (about 1670 feet above tide) feet above New river 

 at Snidow's forr}% were seen in Giles county on the road from the county- 

 seat to that ferry, which is opposite the mouth of Big Stony creek, where 

 the altitude of the water surface is about 1555 feet above tide. The upper 

 plane originally extended far into the recess between Pearis and Sugar 

 run mountains ;* and even now it can be recognized easily in the many 

 hills, whose leveled tops have almost the same altitude. The second 

 plane is more distinct, being better preserved than the other, and having 

 a larger area. Still lower benches, river terraces, were seen, but thej'^ do 

 not exist on the road followed by the writer, and no measurements of 

 their height could be obtained. 



Tiie deposit on the higher planes is sand and clay, carrying vast num- 

 bers of transported polished fragments, most of which are barely three 

 inches in diameter, though some were seen upwards of ten inches. For 

 the most part, these pebbles are of local origin, or, at least, they came 

 from the confines of the "Great Valley," for the sandstones predomi- 

 nate ; but there are not wanting pebbles of glassy and milky quartz, 

 seldom more than four inches in diameter, which must have come from 

 the Blue Ridge, not less than seventy miles away by the nearest water- 

 line. And these are found on the highest bench at nearly three miles 

 from the river's present channel way. 



A fine plane of erosion is well preserved on both sides of New river 

 south from Little Walker mountain in Pulaski and Montgomery counties. 

 Its summit is shown on the west side of the river near Belspring station, 

 with an altitude of not fixr from 1775 feet above tide, the station being 

 1766 feet A. T., while a higher plane is reached along the New River R. R. 

 on this side of the river at the summit cut, two and a half miles from New 

 River station, and about 1925 feet above tide, the track in the cut being 



•For explanation of the relations of the mountains and of most of the localities re- 

 ferrcil to in this paper, the reader is referred to memoirs on Southwestern Virginia, 

 published by tiie writer in Iroc. Amer. Phil. Soc., as follows: Vol. XIX, pp. SS, 219, 

 498; XXII, ]). in, and XXJV, p. Gl. The faults are described summarily in a paper in 

 the Amer. Journ. of Science for April, 1887. 



