658 NEW YORK STATE MUSEUM 



During the period, the area was subject to frequent oscillations 

 of level, marine conditions prevailing during the subsidence, and 

 land and brackish water when elevations occurred. The area 

 of subsidence, however, did not include any portion of the Appa- 

 lachian trough, but was terminated along its eastern side by a 

 decided elevation of the old Appalachian valley fold, and a suffi- 

 cient elevation of the entire Valley trough to bring it perma- 

 nently above sea level. 



West of the Valley fold, and between it and the northeast- 

 ward continuation of the Sequatchie anticline already mentioned, 

 there was a shallow basin that, at least in Pennsylvania, was 

 occupied by a bay. This bay was in existence during the whole 

 or a portion of the time consumed by the deposition of the 

 Pottsville series, and, as it became filled up with sediment and 

 subsidence continued, gradually merged into the main sea. 



