358 
HUBBARD AND CRONEIS 
subsequent weathering of the land surfaces during the later 
Tertiary, producing a layer of loose, insoluble materials. As a 
result of the several rejuvenations discussed on early pages, the 
streams could carry more detritus which was dropped on reach- 
ing lower levels. This process was repeated again and again 
with subsequent uplift and erosion. The sediments now are 
removed from places which have been subjected to severe ero- 
sion but are nearly always present in places where streams are 
too weak to handle the residue. Especially is this true in the 
Pearisburg area where underground drainage takes care of so 
much of the water, that surface erosion is lagging far behind 
subsurface weathering. 
STRUCTURAL GEOLOGY 
The sedimentary rocks of this county have been extensively 
folded, and these folds have their elongated axes roughly parallel 
and trending east by northeast. Many of the upper layers have 
been worn away by erosion, so that narrow, parallel belts of out- 
crops, trending in the same direction as the folds, are the com- 
mon thing. Harder rocks, such as sandstones and quartzites, 
have resisted erosion and hence are the mountain makers. The 
valleys between them are usually carved in softer or more soluble 
strata, such as shales or limestones. 
The folds are, for the most part, continuous and may be traced 
for miles. The same may be said of the faults, which closely fol- 
low the axis of greatest folding. 
Folding has tended to increase the thickness of the formations 
along the crests of the structures and, as a consequence, added 
strength has been given, so that the formation may take up still 
more of the stress. These beds are, of course, competent, such 
as the Clinch, Shenandoah, etc. Non-competent beds, such as 
the Sevier and the Russell, develop smashed, intensely folded 
areas between the stronger layers. Drag folds become pro- 
nounced and small displacements and shearings are common. 
The big Peters Mountain fault runs along the north edge of 
East River and Peters mountains, just outside of Giles County, 
and brings Cambro-Ordovician rocks in contact with upper De- 
vonian strata. A smaller fault parallels the East River-Peters 
Mountain break, and runs north of Wolf Creek. It crosses New 
River just above the rapids at Narrows and proceeds eastward. 
