Stevenson.] iU'i [August 20, 



folds, have at first N. N. W. and S. S. E. dips ; but within a very short dis- 

 tance the direction changes to N. "W. and S. E. ; and the veering toward 

 the east continues until, on the side of Wallen's ridge, the great Trenton 

 limestone dips at N. 80° E., very nearly the same as the strike of the 

 Clinton rocks. Dips of 30 to 60 degrees are common enough on the northern 

 side of the fault, but on the southerly side they seldom exceed 10 degrees. 



The fault of Poor Valley ridge is evidently a cross fault. It continues 

 into Tennessee and is crossed by Powell river. 



The Region hetween Wallen's Bidge and Clinch Biver. — Wallen's ridge 

 and Powell mountain are one in structure ; the valleys separating them 

 are monoclinals ; and the beds shown on Powell mountain reached at 

 one time to the crest of Wallen's ridge, or better, perhaps, to the fault 

 which is the southerly line of the Poor Valley ridge. No detailed 

 examinations were made beyond Powell mountain ; and the notes were 

 obtained only while passing along the Estilville road from the head of 

 North Fork gap to Clinch river. Some details respecting the conditions 

 existing within a few miles further north-east were received from General 

 Imboden. who had crossed Powell mountain into Hunter's valley. 



If the reader will consult the map accompanying Prof. Lesley's memoir 

 of 1872, he will see that Powell mountain curves somewhat sharply toward 

 the south-east near the western edge of the map. This bend is due to ero- 

 sion by a branch of the South Fork of Powell river, and marks no change 

 in geological structure. A similar bend occurs at the North Fork, which 

 is due to erosion by the North Fork of Clinch river. 



There appears to be a general uplifting of the whole area south-westward ; 

 for the dips grow gentler in that direction, and the synclinal between 

 Wallen's ridge and Clinch river seems to grow shallower. The axis of ele- 

 vation curves toward the south-west not far beyond the North Fork gap, 

 and the dip on the slope of Powell mountain becomes south-east. The Car- 

 boniferous rocks do not extend beyond the North Fork gap ; and thence, as 

 far as was examined, only the Upper Silurian rocks are shown on the slope 

 of the ridge ; nothing newer than the Devonian black shales is present 

 along the North Fork of Clinch river after it leaves the gap. Possibly the 

 absence of the later rocks may be due in large measure to erosion. The 

 Carboniferous rocks are well shown on the north-eastern side of the pass, 

 until within two or three miles of the Clinch river. The axis of the syn- 

 clinal was not observed. The Lower Silurian limestone Avas reached again 

 on Stock creek, a tributary of Clinch, which within a mile of its mouth 

 passes under a hill through a large tunnel excavated in the Trenton lime- 

 stone. 



This tunnel is properly regarded as a natural wonder. Its approaches 

 are imposing, and the cliff of limestone, overhanging its mouth, is 

 more than 450 feet high. A railway route was once surveyed through 

 this tunnel, but the line was condemned as dangerous, since huge blocks of 

 the limestone frequently fall from the overhanging cliflF. 



