991 



1881.] , ^LiX. fStevenson. 



begins not far beyond the Little Stone gap and continues thence into Ten- 

 nessee. It was examined from Little Stone gap to nearly three miles be- 

 yond Pennington's gap, a distance of nearly thirty miles, in which it has 

 but two water gaps, those of Powell river and its North Fork, or, as the}"- 

 are commonly known, Big Stone and Pennington's gaps. A wind gap, the 

 Little Stone, affords passage for the turnpike leading from Jonesville to 

 Gladesville. 



In his former memoir, the writer regarded Stone mountain as a fault, 

 but he is now convinced from the conditions observed at Pennington's gap, 

 that the mountain is but the side of an exceedingly abrupt fold, as will be 

 explained in another paragraph. 



In the Poor Valley, which follows the southerly foot of Stone mountain, 

 the Devonian shales are shown underlying the Lower Carboniferous. At 

 the head of the valley, the Lower Carboniferous is well shown in the 

 divide between the South Fork of Powell river and the waters of Stony 

 creek, where it is in direct contact with the Lower Carboniferous of Stone 

 mountain. In the divide, it dips gently toward the south-east, while in 

 Stone mountain the dip is almost vertical, the incline being toward the 

 north-west or north north-west. The dips in the mountain become sharper 

 toward the west, being 70 degrees in Big Stone gap, and 90 degrees in 

 Pennington's gap. The rocks shown in the mountain gaps are the Lower 

 Carboniferous, the Quinnimont group and the lower beds of the Coal 

 Measures. 



The fault of Poor Valley ridge must be described before the structure of 

 Stone mountain can be fully explained. This fault is very nearly parallel 

 to Stone mountain, though the increasing strength of the thrust, by turning 

 the rocks directly on edge, has diminished the interval materially in the 

 vicinity of Pennington's gap. The distance between the two ridges varies 

 from a mile to a mile and a half. At its eastern extremity, the fault be- 

 gins in a gentle anticlinal nearly opposite Little Stone gap. A crack 

 develops in this anticlinal near the gap, by which the South Fork of 

 Powell river crosses it, and increases rapidly in importance westward. 

 The Devonian shales cross the anticlinal at its origin, while in the divide 

 at the head of the valley, the Lower Carboniferous and part also of the 

 Quinnimont group pass over it so as to be continuous with the rocks of Stone 

 mountain. But the anticlinal soon becomes bold, and the fault develops, 

 so that the ridge is divided below the mouth of South Fork of Powell into 

 Poor Valley ridge and Wallen's ridge. There the extent of the fault is 

 sliown, for the Clinton is in direct contact with the middle shales of the 

 Knox group. Poor Valley ridge continues westward to beyond the Ten- 

 nessee line, and varies much in height and width. It is composed chiefly 

 of Clinto?''. rocks, while the Lower Helderberg, Oriskany and Hamilton 

 occur in the narrow valley between it and Stone mountain. 



The writer has stated in another paper that Stone moiuitaiu is a fault, 

 and that it is the continuation of the Clinch river uplift described by Prof. 

 Lesley. Mr. Moore, in the report of his reconnaissance along the border 



