88 Hayes and Campbell—Appalachian Geomorphology. 
unknown. Nevertheless, itseems probable that the earlier period 
was at least eight or ten times as long as the later one. 
DEFORMATION OF THE TERTIARY PENEPLAIN. 
Although the second peneplain was less perfectly developed 
than the first, it has been more perfectly preserved, and so can 
be reconstructed with even greater certainty. The same plan of 
representation has been pursued as in the case of the Cretaceous 
peneplain, and the deformed surface is represented by contour 
lines with an interval of 200 feet; also similar qualifications 
should be made here as in the case of the map representing the 
Cretaceous peneplain. Not all parts are equally reliable by 
reason of differences both in degree of baseleveiing and also in 
the quality of maps and other data upon which it is based. 
The deformation is somewhat exaggerated, especially in the 
interior of the province, for the gradient of the baseleveled 
valleys has not been taken into account. This gradient varies 
with the size of the stream, but present knowledge of baselevel 
conditions is not sufficient to warrant definite statements as to 
the altitude of the baselevel in the interior. Probably the error 
in determining the altitude of the peneplain at any point is 
ereater than the error introduced by neglecting its gradient. 
The contours in plate 5 represent the algebraic sum of all 
movements which have affected the province since the comple- 
tion of the Cretaceous peneplain, while the contours in plate 6 
represent movements which have occurred since the close of the 
Tertiary period of baseleveling; hence the contours of plate 5 
represent. all the deformation expressed in plate 6 plus the de- 
formation occurring between the two periods of quiescence. The 
amount of this intermediate deformation or the vertical distance 
between the two baselevels at any point may be found by sub- 
tracting altitudes indicated by the contours on plate 6 from those 
on plate 5. 
The character of the orogenic activity which followed the com- 
paratively long period of Tertiary quiet is much better known 
than that which followed the longer. Cretaceous period. It is 
much nearer the present than the latter, and the evidence for 
deciphering its history has not yet been obliterated. Part of 
this evidence consists of modified physiographic forms, but the 
larger portion is found in the sediments deposited around the 
seaward margin of the province. We are largely indebted to 
aid 
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