92 Hayes and Campbell—Appalachian Geomorphology. 
rugged gorge 1,500 feet deep, and is still actively corrading its 
channel. The movement along the axis must have been practi- 
cally continuous from the completion of the Tertiary peneplain 
down to the present. 
The region northeast of New river, in which rise branches of 
the Potomac, the James, the Kanawha and the Monongahela, 
has probably been an area of continuous uplift during every 
period of orogenic activity affecting the province. The Creta- 
ceous peneplain, of which only a few doubtful remnants exist, 
was elevated at least 2,400 feet and -Tertiary erosion was propor- 
tionally stimulated. It succeeded, however, only in reducing 
to baselevel and slightly broadening the valleys of the larger 
streams. A post-Tertiary elevation of 1,600 feet has renewed 
their activity, so that it has been continued with scarcely a pause 
from the close of the Cretaceous ‘period down to the present. 
The result of this almost continuous downward stream cutting 
has been to produce the most sharply cut region in the Appa- 
lachian province. The slopes are steep and generally uniform 
from the highest points, which may represent the surface of the 
earlier peneplain, down to the present streams, with only an 
occasional trace of terracing to mark the Tertiary baselevel. 
The elevation of the Tertiary peneplain along the eastern 
border of the province has been only moderate, and the streams 
have accomplished correspondingly little erosion upon its sur- 
face. The Roanoke, the James and the Potomac have cut rather 
narrow and shallow valleys across the piedmont plain. These 
become shallow gorges in the broad baseleveled valleys west of 
the Blue ridge. 
RELATIVE DATES OF THE OROGENIC MOVEMENTS. 
Before closing this portion of the paper it 1s perhaps advisable 
to review hastily, as far as the evidence will admit, the succes- 
sion of oscillations in post-Paleozoic time. As already stated, 
the determination of the character of these movements is one of 
the most important results derived from this study, since the en- 
tire physiography of the region, including the arrangement of its 
drainage systems, has been modified to a great extent by them. 
Movements in the Tertiary Cycle.—It is not advisable at present 
to go farther back in geologic time than to the close of the Cre- 
taceous period of baseleveling, although there are traces of sim- 
similar movements in the preceding ages of post-Paleozoic time. - 
ee 
