1880.] »^7 [Stevenson. 



The Lower Carboniferous. 



Like the Conglomerate, these rocks are found only in the mountains, 

 and details respecting their thickness and composition cannot be ascertained 

 until after the foliage has disappeared. They are shown along the south 

 face of Stone mountain from Little Stone gap westward to the Tennessee 

 line, and on the northerly face of Powell mountain from that gap to the 

 North Fork gap, where the Carboniferous series ends. The Umbral Lime- 

 stone follows the left hand side of the gap until within a short distance of 

 Clinch river. 



No detailed exposure of the interval between the Conglomerate and the 

 Umbral Limestone was discovered, but it is not far from 500 feet thick, and 

 appears to be filled chiefly with red shale, of which a few short exposures 

 were seen. 



The limestone appears as a cliff along the southern face of Stone moun- 

 tain and is well shown on both sides of Big Stone gap, where it dips N. 

 N. W. at 70 degrees, and, as nearly as can be estimated, is between 250 

 and 300 feet thiclc. The turnpike is cut through it at Little Stone gap. 

 Thence, along Powell mountain, it is seen as a broad band to the North 

 Fork gap, where its outcrop bends eastward and follows the left hand side 

 of the gap almost to Clinch river. For the most part, this rock is com- 

 pact and fine grained, but some of the beds are granular. Chert, in nodules 

 as large as an oi'dinary oi'ange, is plentiful in one layer. Fossils occur 

 throughout the mass, but the specimens are not silicified and the species 

 are not readily identifiable. Productus cora and ZapJirentis spinosa were 

 obtained near the mouth of Big Stone gap. Many layers of this limestone 

 are very pure and yield a lime of superior quality. The rock is cavernous 

 and the large caves in Powell mountain afforded a supply of saltpetre to the 

 Confederates during the late war. 



Whether or not rocks of Vespertine age have been brought up along the 

 face of Stone mountain was not ascertained ; but the position of the lime- 

 stone at a few miles west from the Big Stone gap renders probable that no 

 representative of that group has been brought up. On the northerly face 

 of Powell mountain, however, the succession is unbroken and the Vesper- 

 tine rocks are undoubtedly present there, although they are concealed. A 

 coal bed exists in the North Fork gap at a considerable distance below the 

 limestone and therefore belongs to this group. Coal from it was used at 

 a Catalan forge in the gap. 



The Devonian Rocks. 



The immense Devonian series of New York and Pennsylvania is insig- 

 nificant here and is I'epresented only by black shales, which are exposed 

 along the foot of both Stone and Powell mountains. These shales ci'oss 

 the valley near Little Stone gap, where their dip is abrupt near the central 

 line of the valley, but becomes gentler toward each mountain. They are 

 the equivalent of Prof. Safford's "Black shales." Their thickness was 

 not determined accurately, but it cannot exceed 500 feet. No fossils were 

 found in them. 



PROC. AMER. PHILOS. SOC. XIX. 107. M. PRINTED OCTOBER 27, 1880. 



