Stevenson.] *^^ [August 20, 



The Uppek Silukian Rocks. 



The Lower Helderberg, tlie Clinton and the Medina were recognized. 



The Lower Helderberg.— The racks, of this group are exposed in the Poor 

 valley; on the eastern end of Wallen's ridge ; in the valley between 

 Wallen's ridge and Powell mountain ; in the North Fork gap, and on the 

 south-eastern slope of Powell mountain beyond that gap. The exposures 

 are very fair and a complete section could be obtained without much diffi- 

 culty. 



The estimated thickness is not far from 250 feet. For 70 feet from the 

 bottom the series consists of limestones in beds of from three to five feet, 

 separated by shales in somewhat thicker layers. The lower limestones are 

 silicious, but, toward the top, the beds are purer and one of them, black, 

 fetid and four feet thick, contains abundance of Leperditia. Overlying 

 this is a succession of coarse-grained calcareous sandstones, shales and 

 silicious limestones, not well exposed along the line followed in the at- 

 tempt to secure a section. The lower calcareous sandstone is shown in a 

 line of low hills near Big Stone gap, and also on the turnpike within a 

 mile of Cedar gap; the larger of the silicious limestones is shown near the 

 pike opposite the gap, and also on the north side of Powell river at barely 

 a mile below the gap. It is very light in color and has a cherty look. 

 Immediately above it is a coarse reddish-gray sandstone, closely resembling 

 the Oriskany sandstone of New York. 



The lower sandstone is well shown on the pike, Avhere it seems to be 

 made up almost wholly of casts of OnMs oblata, Bhynchonella ventricosa, 

 and undetermined Meristella. 



The silicious limestone jnelded Grinoid stems, abundant ; Aspidocrinus 

 scuteUiformis ; Ghcetetes ; Favosites ; Atrypa reticularis; Strophomena 

 rliomboidalis ; Strophodonta ; Spirifer cyclopterus ; Meristella; Rhyn- 

 chonella nucleolata ; Orthis oblata; and other forms which were not 

 recognized. 



The immediately overlying sandstone has a broad Meristell-t ; Spirifer 

 perlamellosa ; Fdvosites ; Caninia helderbergim ; the last two in great 

 abundance. 



At some distance up tlie valle3% say four miles above the Big Stone gap, on 

 property belonging to Mr. Spencer, the upper silicious limestone becomes 

 impregnated with brown hematite. Usually only the joints have been 

 filled, but occasionally for considerable distances the rock has been replaced 

 by limonite. The ore is too silicious to be of any value. The fossils are 

 distinct. Along the valley between Wallen's ridge and Powell mountain, 

 the Lower Helderberg rocks can be followed easily ; the silicious limestone 

 and the lower calcareous sandstone have been replaced to a greater or less 

 extent by brown hematite. The outcrop of the lower ore follows the hillside 

 above the road for miles, while the upper bed follows the creek-bottom 

 almost to the head of Wildcat creek. Much of the ore at the upper horizon 

 is exceedingly poor, but there are some pockets of decidedly good material. 

 The fossils are the same with those seen at the same horizon in the Poor 



