GEOLOGY OF GILES COUNTY, VIRGINIA 
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inches. Joints are rare. There are calcite nodules but no veins 
and no chert. Fossils in a layer of thin black shale one foot below 
the top of the horizon. Weathers lighter than the rock to yellow. 
7 feet, 
42. Upper, mottled layer with light and dark grey in lines, 
bars and blotches. Crystalline and coarse grained more pro- 
nounced grains than in the lower mottled layer. There are a 
few calcite crystals and veins. No chert. Some oblique and 
irregular joints. One layer only. 2% feet. 
43. Upper, light steel gray layer of limestone. Fine crystal- 
line with conchoidal fracture. The bedding planes are rarely 
smooth, some being fluted or pitted like waffle irons. Calcite 
veining in the joints, and there are shale partings between some 
of the layers. Calcite crystals are common in the upper portion. 
Two feet from the base there are quartz crystals, iron oxide and 
an unidentified green mineral. Weathers light. Fossils were 
found in this member in 1923 consisting of brachiopods, cephalo- 
pods, a simple coral one inch in length and the pygidium of a 
small trilobite. 11 feet. 
44. Bluish to dark steel gray, massive but medium bedded 
limestone whose layers are two inches to three feet thick. It is 
crystalline and looks like chert but is quite free from it. Joints 
are rare and the fracture is uneven to conchoidal. Calcite 
crystals occur in nodules and a few veins. Weathers lighter than 
the rock to yellow. 4 feet, 5 inches to 10 feet, 8 inches. 
Total thickness 609 feet. 
This division does not complete the Shenandoah, but it is as 
final as can be made in this area. Unit 44 is just below the 
Chickamauga but unit 1 is an undetermnable distance above the 
top of the Russell. 
THE ORDOVICIAN SYSTEM 
Introduction 
Ordovician rocks are widely distributed in Giles County, form- 
ing parts of the valley floor and sometimes capping lower ridges. 
The series grades from limestone at the base to sandstone at the 
top, and shows a distinct graded transition; limesone to argil- 
laceous lime to shale then to arenaceous shale, which gradek 
further into shaly sand and at last becomes a distinct sandstone 
in the Bays. 
