Pensauken Formation — Description. 71 



giving the streams a greater gradient, or because the streams 

 carried less detritus, owing to a change in climatic or other 

 conditions within their basins. 



Erosion of the formation. — When deposition ceased, the pres- 

 ent systems of drainage established themselves on the new de- 

 posits. Subsequent erosion has destroyed the flatness of the 

 depositional surface by developing valleys of varying sizes be- 

 low it. In places considerable undissected areas of the forma- 

 tion remain, and in such places the' surface is nearly flat, as in 

 the vicinity of Prospect Plains, northeast and west of Hights- 

 town, north of Hartford, and northeast of Moorestown. These 

 areas probably represent, approximately, the original surface of 

 the formation. But in many places erosion has gone so far that 

 the surface has been much dissected, and the topography ad- 

 vanced to maturity, and, locally, to old age. Many of the val- 

 leys have been cut through the formation into underlying beds, 

 and in not a few cases the valleys in these underlying beds are 

 wide. 



Even in the Raritan Bay-Trenton-Salem valley, where the for- 

 mation was best developed, it is restricted largely to the divides 

 between the streams. Generally speaking, its areas are broad 

 where the divides are broad, as between South River and Cross- 

 wicks Creek, and narrow where the divides are narrow. The 

 remnants of the formation are so disposed as to show that it was 

 once continuous between the areas where it now occurs, and that 

 its dissected condition is the result of stream erosion. 



Southwest of Crosswicks Creek, the broad valley plain on 

 which the formation was best developed is crossed by numerous 

 tributaries to the Delaware, whose courses are roughly from 

 southeast to northwest. These streams have not only cut through 

 the Pensauken, but they have removed much of it, and the areas 

 remaining stand in somewhat definite relations to the streams 

 which flow directly to the Delaware, being elongate on the di- 

 vides between them. But in many cases another factor influences 

 their position. Many of the remnants of the formation here have 

 a pronounced northeast-southwest linear arrangement, in dis- 

 regard of the courses of the streams. This arrangement is de- 

 termined bv the underlying formations, which have influenced, 



