SILUEIAN. 231 



m southwestern Virginia, in the Pocahontas quadrangle, Campbell ^^ did not 

 distinguish the "Monterey" sandstone (Oriskany) and Lewistown limestone but 

 named the strata which occupy the interval between the Clinton and the Devonian 

 the Giles formation. His section is as follows : 



Feet. 

 Giles formation (Oriskany and Lower Helderberg [Devonian]): Coarse yellow sandstone, 



cherty limestone, coarse reddish sandstone, blue limestone 30-200 



Rockwood formation (Clinton): Heavy sandstone or quartzite, sandy shale and ferruginous 



sandstone with siliceous red fossil ore and hematite 20-400 



Clinch sandstone (Upper Medina): Coarse white sandstone or quartzite 150-250 



Bays sandstone (Lower Medina) [Ordovician]: Red sandstone and sandy shale 250-350 



The Giles formation comprises strata which are grouped because they are 

 usually covered and can not be distinctly traced. In the Kimberling Wilderness, 

 in the eastern part of the Pocahontas quadrangle, Campbell recognized the following 



divisions : 



Section of the Giles formation [Devonian]. 



Feet. 

 Greenish sandstone locally containing pebbles of the limestone at the base of the group; thick- 

 ness not determined. 



Cherty limestone or chert 30-40 



Coarse ferruginous sandstone locally composed of small quartz pebbles cemented by iron oxide. 15-20 

 Blue limestone, shaly at the base 30-40 



At the boundary between Virginia and Tennessee (in the Bristol quadrangle) 

 the Silurian consists of the Clinch and Clinton or "Rockwood" formations, together 

 with the Hancock limestone (Silurian and Devonian). Here the Bays, Ordovician 

 (350 to 450 feet), and Clinch (250 to 450 feet) are thicker; the Clinton or "Rock- 

 wood" (200-300) is similar in thickness to the last section cited. The characters of 

 these formations remain the same. 



The Hancock is a blue f6ssiliferous cherty limestone. It also appears in the 

 northwest corner of the Morristown quadrangle, Tennessee, in latitude 36° 30' 

 north, longitude 83° 30' west, but does not occur farther south. Keith*" states: 



In the Powell syncline are found the only areas of this formation [the Hancock limestone] 

 in the valley of east Tennessee, and from its occurrence here in Hancock County it derives its 

 name. The formation consists entirely of interbedded massive and shaly limestgnes of a blue, 

 gray, or dove color. Massive beds are more frequent at the bottom and top of the formation 

 and attain a thiclcness of 20 feet.. Great numbers of fossils, largely brachiopods, corals, and 

 crinoids, are found throughout the formation and show it to be of upper Silurian [Helderberg, 

 Devonian] age. 



In the Greeneville quadrangle, Tennessee (longitude 82° 30' to 83° west, 

 latitude 36° to 36° 30' north), east of the Morristown quadrangle, the Silurian 

 comprises the CUnch and part of the Clinton ("Rockwood"). The section as 

 given by Keith **^* is as follows: 



Feet. 



Rockwood formation: Green, red, and yellow sandy and calcareous shale 700+ 



Clinch sandstone: Massive white sandstone 300-500 



Bays sandstone [Ordovician]: Massive and shaly red sandstone 50-400 



In the northwestern part of the quadrangle the C!linton ("Rockwood") is 

 lacking and the Chattanooga shale (Devonian) rests on the eroded Clinch sandstone. 



In the Briceville quadrangle, 60 miles west of the Greeneville, the Bays (Ordo- 

 vician) is a "red argillaceous and sandy limestone, 160 to 200 feet thick;" the 

 Clinch sandstone is absent, and the CUnton ("Rockwood"), which rests conformably 



