GEOLOGY OF GILES COUNTY, VIRGINIA 339 
The Sevier Shales 
This formation, showing the transition from limestones to 
sandstones above, forms the steep slopes of the larger valley 
ridges. It takes its name from Sevier County, Tennessee and 
corresponds with the late middle and upper Ordovician of New 
York, that is, the late Utica and Eden shales. It is also probably 
equivalent to the Maquoketa shales in Iowa as well as part of 
the lead and zinc bearing formations known as the Galena lime- 
stones. 
This formation, which varies from calcareous shales at the 
base to sandy shales at the top, is from 1250 to 1500 feet in thick- 
ness, the section at the Narrows measuring 1341 feet. 
These shales are fossiliferous throughout, corals, graptolites, 
sponges, bryozoans, and cephalopods being found rather com- 
monly. In the upper layers trilobite fragments are found and 
pelecypods are common. Brachiopods are found throughout. 
Plectamhonites sericeus is especially numerous and seems to be 
characteristic of certain beds in the formation. 
The shales are interbedded with thin limestone layers in many 
places, and on the whole the formation is weak and non-resistant 
as well as being thin bedded throughout. Like the Russell forma- 
tion, these shales are also folded and contorted. The bedding is 
clearly defined but the jointing is not conspicuous except where 
it forms cuneiform pits. Blue, brown, green and gray color com- 
binations are the most common ones, with calcite veining rather 
marked in some places. 
This formation passes up into the overlying sandstones rather 
abruptly and thus the dividing line is not so difficult to establish 
at the top as at the bottom, where Moccasin conditions seem to 
reappear several times after many feet of Sevier shales. 
Paleontology and Correlation 
In Sevier County, Tennessee, the formation overlying the 
Tellico, has been named the Sevier. This formation is not very 
fossiliferous ordinarily, but has a fairly well developed fauna 
in Giles County. Fragments of Triarthrus becki, Plectamhonites 
sericeus, Rafinesquina alternata, R. squamulata, Calymene sp. 
and Zygospira sp. are most commonly found but both Diclymo- 
graptus and Monogmptus types of graptolites are also present. 
From the faunal evidence, the shales are late middle or upper 
