1881.] ^^ • [Stevenson. 



of the several subordinate ridges in both Copper and Moccasin ridges. 

 Those cherty beds, too, are iron bearing, and eacli of them carries ex- 

 tensive deposits of brown hematite, some of whicli have been explored. 

 The lowest bed of this division is a calcareous sandstone very similar to 

 that at the base of the group. 



The middle division consists mostly of shales, with which are beds of 

 impure limestone, more or less silicious and varying from 2 to 10 feet in 

 thickness. This is shown along Clinch river at many places as well as 

 along Stock creek and along the Jonesville and Estillville road as it passes 

 from the North Fork of Clinch river to the mouth of Stock creek. 



The lower division is a mass of calcareous sandstone and sandy lime- 

 stones with some shale, the whole containing great quantities of iron 

 pyrites, which makes up fully one-fifth of the whole mass of some beds. 

 This mineral occurs in irregular laminse often one-fourth of an inch thick, 

 which sometimes make a network on the exposed surface of the rock. 

 This division is well exposed along the whole line of the Hunter Valley or 

 Clinch uplift within the region examined. 



The composition of the Knox group here is approximately as follows : 



1. Limestones, shales and chert beds 1750' 



2. Shales and limestones 1000' 



3. Calcareous sandstones, pyriferous 500' 



Thus giving for the whole group a thickness of not far from 3250 feet. 



III. Geology of the Area Drained by Powell River. 



The important coal-field lying north from Stone mountain narrows 

 rapidly westward owing to the convergence of Stone and Black mountains, 

 so that, as far as Virginia is concerned, it practically disappears at but a 

 little way beyond Pennington's gap. But the available area diminishes 

 •even more rapidly. The streams flowing from Black mountain become 

 shorter, and have a greater fall, so that, as the beds dip toward Black 

 mountain, the area above natural drainage is much smaller even propor- 

 tionately on the waters of the North Fork of Powell than it is along those 

 forks which unite at the head of Big Stone gap. 



The previous memoir by the writer contained a section of the Coal 

 Mea&ures as they appear above Big Stone gap ; but the lower part was 

 given according to a rude estimate, while 500 feet at the top had not been 

 examined in detail. As already intimated, the unexamined part at the top 

 is much greater than is given in that section. As amended, according to 

 observations at the head of Pennington's gap and according to Mr. Moore's 

 barometric determination of the height of Black mountain at the head of 

 Looney branch of Cumberland river, the section is : 



1. Not examined 800' 



2. Sandstone and sandy shale 200' 



3. Coal bed 0' 4" 



4. Sandstone 30' 



5. Goal bed 1' 5" 



6. Sandstone and shale 115' 



