248 C P. BERKEY PALEOGEOGRAPHY OF SAINT PETER TIME 



became a waste of drifting sands; but a deep bay extended northward to 

 the southern boundary of New York, as appears from records of undis- 

 turbed sedimentation in Center county, Pennsylvania. 



4. A readvance of the sea northward to the vicinity of its original 

 position followed. In this movement the sands that had been dragged 

 out by the retreating sea and carried out by streams or transported in 

 large part by winds were worked over, given their characteristic struc- 

 tures, and such fossils as belong to the formation were buried in them. 

 The natural break representing the time interval, that would have been 

 preserved in almost any other type of rock, is largely obliterated. With 



Figuue 5. — Continental Outline at maximum Retreat of the Seas in mid-Saint 



Peter Time. 



the oscillation, except locally along the margin, there is no evidence of 

 unconformity of angle on a large scale. It appears also that in most 

 localities the sea must have Avorked over almost the whole sand mantle, 

 while in others the difference above and below the chief zone of disturb- 

 ance may be the foundation for the occasional suggestion that has been 

 made to divide the formation into an upper and a lower Saint Peter. 



