GEOLOGY OF GILES COUNTY, VIRGINIA 
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conglomerates, breccias and sandstones. The latter are some- 
times metamorphosed partially into semi-quartzitic divisions. 
Most of the ridges are capped by the Clinch sandstone, which 
is a very resistant division of the Silurian, while the valley floor 
is usually the Shenandoah Limestone. Outcrops are often de- 
creased or made wider by the complex folding and faulting. 
On the following page is a table of the formations found in 
Giles County. 
THE CAMBRIAN SYSTEM 
Introduction 
The Cambrian of Giles County is made up of limestones and 
shales in the lowest division, and of limestone and dolomite in 
the upper portions. The Middle Cambrian time seems to have 
been one of erosion in this area, although the unconformity be- 
tween the Lower Cambrian Russell and the Upper Cambrian 
Shenandoah is not marked. Deposition was continuous from 
Upper Cambrian on into Ordovician time, hence the great Cam- 
bro-Ordovician limestone series. 
The Russell Formation 
The Russell Formation, composed of variegated shales, massive 
and impure limestones, takes its name from Russell County, Vir- 
ginia, where it is found developed to its fullest extent. It is 
probably equivalent to Apison and Rome formations of Southern 
Tennessee. 
In the Pearisburg section, it is brought in over a small area 
running with slight variation east and west through Bane, by 
the large anticline between Pearis and Walker mountains. In 
this exposure, it is non-fossiliferous but in some localities* it 
carries the Olenellus fauna of Lower Cambrian time. The forma- 
tion passes from medium bedded, resistant, blue gray, blotched, 
limestone at the base, through highly colored green and choco- 
late shales and intermediate limestone lenses and layers, to 
greenish and yellow shales, which, in some places, grade directly 
over into the Shenandoah formation but in other places are 
separated from it by several feet of white and gray calcareous 
shales. 
Four small anticlines, the largest of which is approximately 
* Russell County, Virginia. 
