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HUBBARD AND CRONEIS 
the v*alley they are carried south. They are also present over a 
considerable area in the eastern as well as the western mountain 
areas, but their outcrop on the Walker Mountain range lies only 
in a narrow strip which is very restricted in Giles County. 
The Clinch and the Rockwood are both mountain making rocks 
and they are usually found capping ridges. Iron ore of the Clin- 
ton type is found in the Rockwood but has not been exploited to 
any extent here. There are about 550 feet of Silurian strata in 
Giles County. 
The Clinch Sandstone 
The Clinch Formation, taking its name from Clinch Moun- 
tain, is found throughout the entire Appalachian system. It 
corresponds to the Medina Sandstone of New York. All the 
important valley ridges owe their existence to this heavy plate 
of sandstone which has preserved summits at or nearly at the 
level of the oldest recorded peneplain, while adjacent areas have 
been eroded to the present valleys. 
This formation is easily separable from all the others because 
of its massive character. It usually varies between 125 and 300 
feet in thickness, there being 140 feet in the Narrows exposure. 
This rock is a semi-quartzitic sandstone, coarse to fine grained, 
sometimes conglomeratic with large quartz pebbles. Slicken- 
sides are rather common because the beds are so stiff that they 
break and slide over each other rather than bend. The formation 
weathers light brown to yellowish bronze color, red and purplish 
red occurring in places. It has an uneven fracture, is fairly even 
bedded, and very dense and resistant. These rocks form the 
larger rapids at the Narrows of the New River. 
The formation contains arenaceous shale layers which be- 
come more numerous towards the top. While fucoids are found 
in some places, the formation may be regarded as practically non- 
fossiliferous. 
Paleontology and Correlation 
The Clinch thickens off to the north and east, so that while 
in Giles County its thickness is 140 feet, it is 300 feet thick in 
northern Virginia where it makes Cacapon Mountain. On Mass- 
anutten Mountain, sandstones of equivalent age are called Mass- 
anutten, while in Pennsylvania and Maryland, the same forma- 
tion is known as the Tuscarora sandstone. 
