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plain corresponds roughly to the Upland peneplain of Stose and 
the Kittatinny peneplain. The elevations grade from 3100 feet 
in Virginia to less than 2000 feet in Pennsylvania. The Inter- 
mediate peneplain, as described by Stose, is in Giles County 
developed as the Buckeye Peneplain, which here is some 250 feet 
higher than farther east. The Valley-floor base level of Stose, is 
the Pearisburg Peneplain of Giles County. Here it is 100-200 
feet higher than it is to the east in the Valley of Virginia. 
Since Jurassic time it is evident that Giles County has been 
elevated some 3000 feet. The most widespread peneplain was 
the first. The later ones were successively smaller and more in- 
complete. The present drainage is about 1500 feet above sea 
level. A peneplain this far from the sea would probably stand 
300-400 feet above sea level. 
Underground Drainage 
A very prominent feature of this area is the sink hole topog- 
raphy. As has been mentioned before, the U. S. G. S. map of 
1884 does not indicate any depression contours. However, these 
sinks develop with considerable rapidity, some of the older natives 
recalling a half a dozen of ordinary size which have appeared 
during their life time. The writers do not from this intend to 
convey the idea that the sinks were too small to be mapped in 
1884. Their omission from maps of this issue is regarded as 
the result of the reconnaissance nature of the mapping, or to 
the fact that, at that date, no depression contours were used on 
any maps. 
Sinks are confined to the limestone areas of Giles County. 
So common are they, that they can be of use in determining the 
outcrop of the Shenandoah and Chickamauga formations, to 
which horizons they are limited. Caves are invariably found at 
the bottom of the sinks. The latter have been formed by the 
falling in of the roofs of solution passages, which ordinarily 
have formed along joint plains. Some of the caves are so ex- 
tensive that it is possible to travel many hundreds of yards 
through their various passages. 
In many cases, the surface drainage is in the reverse direction 
of the underground, so that when an entire series of sinks 
develop along prolonged joint planes (as they often do), the 
surface drainage is reversed. As a result of this underground 
