waa? ae eee eS 
i, 
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The Peneplain in Virginia. 7) 
is not so well marked as about Asheville. Considerable study 
has been given to the region just north of this province by Davis, 
who suggests in the paper above cited* the probability of the 
extension of the Cretaceous peneplain over the entire southern 
Appalachians. Though he makes no definite statements as to 
its elevation and attitude, yet he concludes that the summits of 
the Blue ridge, south of the Pennsylvania line, probably repre- 
sent this baselevel. The present writers have searched quite 
carefully for definite evidence as to the existence of the pene- 
plain in this region and so far have been unable to find any- 
thing entirely satisfactory. That the region in question was 
baseleveled is conceded by all who are familiar with its topog- 
raphy, but the present elevation and attitude of the peneplain 
are less certain. Southeast of the Blue ridge there are a few 
outliers or isolated knobs standing above the Tertiary plain, 
and these show a uniform altitude of about 1,000 feet. It 
seems scarcely possible that these outliers should have been 
reduced to so nearly a common level unless that level were the 
baselevel of erosion. Immediately north of the Blue ridge, the 
Massannutten mountain shows traces of baseleveling at alti- 
tudes varying from 2,400 to 2,500 feet, and the valley ridges 
to the northward probably show traces at still greater altitudes. 
The Blue ridge varies greatly in altitude; its crest rises toward 
the south from 1,200 feet at Harpers Ferry to 4,000 feet at the 
Peakes of Otter, in central Virginia, and toward the north to 
2,300 feet on the Maryland-Pennsylvania line. If there were a 
corresponding gradient in the peneplain it would necessitate a 
deformation along a cross-axis, of which there is no trace further 
westward ; also the crest line of the Blue ridge between the points 
mentioned is extremely irregular and bears no resemblance to 
the remnant of a baseleveled plain. The varying elevations of 
the plain, determined on either side of the Blue ridge, agree with 
certain features of the ridge itself and make it decidedly probable 
that the peneplain here is highly tilted eastward; the strike of 
the plain—i. e., the direction of the contours representing the 
restored surface—crosses the ridge at a low angle instead of being 
parallel with it. The result of these complex conditions is that 
no two remnants of the old plain are found along the trend of the 
ridge at the same altitude. and consequently they are extremely 
difficult to recognize. Assuming this attitude of the peneplain 
* Bull. Geol. Soc. Am., vol. ii, 1891, p. 562. 
