1880.] 



89 



[Stevenson. 



mountain. Unfortunately, there was no opportunity to make accurate 

 measurements of horizontal distances and the scale of the cross-sections is 

 probably somewhat distorted. In neither case was Powell mountain 

 crossed along the line of section and the details respecting its southern side 

 are tal^en from features observed in the North Fork gap. 



The western section is shown in Fig. 1. 



Fig. 1. — Cross-section from crest of Black Mountain to south-eastern side of 

 Powell Mountain, a, Black Mountain; b. Stone Mountain; c. Poor Valley 

 Ridge; rf, Wallen's Ridge; e, Powell Mountain; /', Stone Mountain fault;/", 

 fault of Poor Valley Ridge. 1, Coal Measures; 2, Conglomerate; 3, Lower Car- 

 boniferous; 4, Devonian; 5, Upper Silurian ; 6, Lower Silurian. 



Beginning at Black mountain, one finds himself amid the Coal Measures ; 

 going soutliward, he sees a slow but steady increase in dip until, as he ap- 

 proaches the Big Stone gap, it becomes nearly two degrees. But there the 

 increase is very rapid, so that at the liead of the gap the Serai conglomer- 

 ate is dipping north-north-west at 80 degrees. The Lower Carboniferous 

 limestone forms a bold cliff on both sides near the mouth of the gap and 

 dips in the same direction at 70 degrees. Here a fault occurs, and one 

 comes at once to black shales of unknown thickness, dipping in like direc- 

 tion at barely 30 degrees. Below these are the Lower Helderberg rocks, 

 well exposed and of considerable thickness. On the south side of the Poor 

 valley, and the northern slope of Poor Valley ridge, are the Clinton rocks 

 with the fossiliferous ores, which continue to the head of Cedar gap, 

 through wliich one comes to Turkey cove, separating Poor Valley ridge 

 from Wallen's ridge. At the liead of this gap, one crosses another fault 

 and soon comes to the Trenton limestone, which is pressed into man\' short, 

 close curves, bixt finally takes an almost due east dip on the northerlj'' face 

 of Wallen's ridge. Tlie Medina sandstone is shown on the crest of that 

 ridge, wliile the ClintiMi and Lower Helderderg rocks are well exposed in 

 the valley between Wallen's ridge and Powell mountain. The black 

 shales appear in the side of the latter ridge, with the Lower Carboniferous 

 limestone higher up and the Conglomerate at the crest. On the opposite 

 side of the mountain Hunter's valley is reached and there one finds the 

 Coal Measures. 



The other section, extending from the crest of Stone mountain to that 

 of Powell mountain, is not more than seven miles distant from the other 

 section, but it shows a great difference in the structure. 



PKOC. AMER. PHILOS. SOC. XIX. 107. L. PRINTED SEPTEMBER 9, 1880. 



