GEOLOGY OF GILES COUNTY, VIRGINIA 
313 
Brushy and Spruce Run mountains, as well as portions of 
Walker, Peters and Flat Top mountains have a height of approx- 
imately 3100 feet. This is the probable elevation representing a 
second base level which was only partially completed in Cretace- 
ous time. This old base level will be referred to as the Spruce 
Run Peneplain. 
A third and still less extensive base level was partially reached 
in early Tertiary time (probably late Eocene). This old surface 
is represented by heights in Buckeye Mountain, and by numerous 
spurs on all the mountains having the uniform height of about 
2500 feet. This base level will be called the ‘‘Buckeye Peneplain'' 
in this report. 
A fourth, and last base level, which was in all probability 
reached in late Tertiary time, is represented by the numerous 
elevations in Giles County of approximately 2100 feet. This 
valley floor peneplain will be referred to as the “Pearisburg" 
base level. Remnants of this old surface are better developed 
in Monroe County to the north than they are in Giles, however, 
much of the land about Pearisburg and at various points along 
New River stand at this elevation. On this level are quantities 
of gravel, sands and clays of fluviatile origin. 
In latest Tertiary and in Quaternary time. New River has cut 
its present gorge in this area. Work towards the ultimate base 
level has scarce begun, yet the valley has been incised at least 
400 feet. In the future, lateral planation will exceed vertical 
cutting in this county, because the New River is regulated by 
the natural quartzite dam across its valley at the Narrows. This 
resistant rock can be cut only very slowly, so that above the 
Narrows the limestone valley probably will continue to broaden 
rather rapidly. 
The peneplain surfaces in Giles County are not so well deflned 
as they might be, yet it is possible to make a rough correlation 
of the base levels recognized here with those described by Stose 
and Miser® as occurring in the Valley of Virginia. 
The Upper peneplain at 3500 feet is undoubtedly the same as 
the Summit Peneplain of Stose and Miser, at an elevation of 
3000-3800 feet. This base level is regarded as older than the 
Kittatinny peneplain of Pennsylvania. The Spruce Run pene- 
® Stose, G. W., and Miser, H. D., Va. Geol. Surv. Bull. 23. “Manganese 
Deposits of Western Virginia,” 1922. pp. 20-22. 
