CYCLES OF EROSION IN THE PIEDMONT PROVINCE 
OF PENNSYLVANIA* 
F. BASCOM 
Bryn Mawr, Pennsylvania 
Since 1912, when Professor Barrell brought to the attention of 
the Geological Society of America some conclusions opposed to the 
earlier interpretation of the erosion history of certain portions of 
the Appalachian highlands, the writer has had in mind the possible 
application of similar conclusions to the erosion history of the 
Piedmont province of Pennsylvania. The results of this intention 
are presented in this paper. The conclusions reached are not 
precisely in accord with those enforced with so much originality 
by Professor Barrell, nor do they involve much that is new in the 
interpretation of the erosion history of eastern Pennsylvania, but 
they are presented as a record of the present stage of the study 
of the peneplains of the Piedmont province of Pennsylvania. 
' Jt is the purpose of the paper to call attention to the fact that — 
the erosion history of eastern Pennsylvania as indicated by altitudes 
and by the record of sedimentation must have been complex, that 
it was made up not of one or two or three cycles of prolonged 
erosion, but of many interrupted cycles, and that vestiges of nine 
of these cycles testify to their reality. Other cycles may have 
existed and probably did exist, but too briefly for permanent 
record. Six of these nine cycles are thought to belong to post- 
Cretaceous time and three to Cretaceous time. 
The question of the subaerial or marine origin of these pene- 
plains is debated, but decisive criteria are lacking for a final pro- 
nouncement. 
t Published by permission of the Director of the United States Geological Survey. 
The writer takes pleasure in acknowledging her indebtedness to M. R. Campbell and 
G. W. Stose of the United States Geological Survey for helpful comments and queries 
made on the subject-matter of this paper, and to Professor W. M. Davis for valuable 
specific suggestions. 
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