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ROLLIN T. CHAMBERLIN 



first few thousand feet would be likely to be more than offset by the 

 probable error in projecting folds to such a distance from the observed 

 dips. 



For the division from Tyrone to Mount Union (Figs, i and 2) 

 the thin, but strongly resistant Oriskany sandstone was chosen for 



Fig. I. — A reconstruction of the folded section from the essentially horizontally 

 bedded uplands west of Tyrone nearly to Petersburg. East of Tyrone the dip-angles 

 are plotted on the horizontal line which represents the railroad-level; on the uplands 

 west of Tyrone they are plotted according to the surface topography. The numbers 

 representing the formations are those used by the Pennsylvania Geological Survey 

 II, Trenton and Calciferous; Til, Hudson River shales; IV, Oneida and Medina 

 V, Clinton; VI, Lower Helderberg; VII, Oriskany; VIII, Chemung; IX, Catskill 

 X, Pocono; XI, Mauch Chunk; XII, Pottsville conglomerate. 



Fig. 2. — Continuation of section from Petersburg to Mount Union 



measurement as likely to give the most reliable results. In the second 

 section the Oriskany was also measured as far as the crest of the 

 anticline just before the prominent fault near Iroquois Station (Fig. 4). 

 At the very crest-point of this anticline the measurement was shifted 

 from the Oriskany to the base of the Catskill since the strata soon 

 take a tremendous dip which carries the Oriskany far below the 

 surface. This shift appears permissible since the fold is approxi- 



