CYCLES OF EROSION IN PENNSYLVANIA 
to be such an inland extension of erosion 
during the Sunderland cycle. 
In general the Sunderland extends from 
faeroo to the 180 contour limes: the 
Wicomico from the 80 to the 90 contour 
lines, and the Talbot, where it does not 
coalesce with the Wicomico, from the 
40-foot contour to sea-level. These three 
terraces are conspicuously developed in 
eastern Pennsylvania parallel to Delaware 
River. In Maryland the Wicomico and 
Talbot terraces are in some places oblit- 
erated and the Sunderland reaches the 
edge of the beach with a cliff 100 feet high, 
but this is not the case in Pennsylvania 
where the terraces are not seacoast 
features. 
The Wicomico terrace wraps about the 
Sunderland as the Sunderland does about 
the Late Brandywine, with usually a well- 
marked break between the two, except in 
the gorges of the tributary streams. The 
Talbot terrace borders the Wicomico, 
which it penetrates along drainage ways, 
and in some places parallel to Delaware 
River coalesces with the Wicomico. 
It has not proved practicable to show 
by graphic means the distribution of the 
remnants of the peneplains and terraces 
in the Piedmont province of Pennsylvania. 
It may be stated that in general the oldest 
peneplain is farthest inland and the young- 
est nearest the shore, with those of inter- 
mediate age ranging between. If this 
region had been one of uniform resistance 
to weathering, there would have been a 
perfect operation of this law of areal 
Cross Section 
Schuylkill River and Wissahickon Creek 
Early Brandywine 
Brandywine 
Late Brandywine 
500° Early Brandywine 
Q' 
1000’ 
750' 
250' 
Fic. 22.—Section crossing Schuylkill River and Wissahickon Creek 
557 
