ISSi.] Jo7 [Stevenson. 



Tlie Silurian or Zipper Silurian. 



Clinton and Medina alone represent this age within the area examined. 

 In Scott, Lee and Wise counties the Oriskany and Lower Helderberg are 

 exposed repeatedly by faults there developed on the easterly side of the 

 Stone Mountain anticlinal. Those groups were recognized even under 

 the Clinch fault on Stony creek in Scott county ; but they evidently thin 

 out somewhere between the Clinch fault and Clinch mountain and their 

 disappearance eastward is equal!}' well-marked. There is no reason to 

 suspect a fault between Clinch mountain and Brushy mountain ; on the 

 contrary, the succession of Clinton, Hamilton and Chemung is shown on 

 the bluti' northerly side of Brushy mountain at nearly two miles east from 

 Laurel Fork gap ; many petty gaps show conformability throughout and 

 that the Clinton passes gradually into the Hamilton. The same condi- 

 tions are shown in passing from Big to Little Walker mountain. Beyond 

 doubt, the Clinton is reached on Dump creek. Dry fork of Sandy and 

 Cavitl's creek, but no Oriskany was observed on any of those streams, 

 nor was anything seen which could be referred to the Lower Helderberg, 

 except possibly a limestone found on Dry fork of Sandy at half a mile 

 above the Stony Ridge fault. The disappearance of these groups in a 

 south-eastward direction is in great contrast with the great thickening of 

 the Lower Carboniferous and Devonian in the same direction. 



The Clinton forms a bench on the southerly slope of Big Walker and 

 Clinch mountain sand is the surface rock in much of the Poor valley fol- 

 lowing the foot of each mountain. Narrow strips occur along the crests 

 of Paint Lick, East River, Dial, Deskins and possibly of House and Barn 

 mountain. The group consists of variegated shales with the whitisli 

 sandstones which everywhere lie near the fossil ore and are characteristic 

 of the group through its extent. The fossil or "dyestone" ore is present 

 on all the mountain mentioned. Limestone appears to be wholly absent. 

 The thickness of the group was not ascertained, but it cannot be less than 

 1000 feet. 



The Medina forms the crest of Big Walker montain ; of Clinch moun- 

 tain, and its outliers, Rich, Garden, Short, Little Bear Town and Brumley ; 

 of House and Barn mountain ; and it makes a double outcrop near the 

 summit of Paint Lick and East River mountains. 



The upper or white Medina, in irregular laj'ers and from 200 to 300 feet 

 thick, forms jagged cliffs. It contains a few thin layers of conglomerate, 

 but, for the most part, the rock is very far from being coarse and some of 

 the upper layers weather with polished surface. No fossils were seen aside 

 from the characteristic Arthrophycus harlani. 



The lower Medina, a mass of red to reddish-brown sandstone and shale, 

 forms a terrace on the sides of the Medina ridges. It does not differ from 

 the beds recognized as lower Medina in the central tier of counties in 

 Pennsylvania, where it is sometimes called the terrace formation. The thick- 

 ness is not far from 400 feet ; but at all exposures the group is so badly 



PROC. AMER. PHILOS. SOC. XXII. 118. R. PRINTED MARCH 2, 1885. 



