Pensauken Formation- — Description. 73 



veloped by tributary streams which flowed northwestward to the 

 trunk stream which then flowed through the Raritan Bay-Trenton 

 valley. This part of the plain of erosion, therefore, sloped 

 gently from the southeast to the northwest toward the axis of 

 the main valley. At the southeast the broad plain of degradation 

 was limited by a low scarp, the slope of which was much greater 

 than the slope of the plain to the main stream. 



Aside from these low slopes which the plain possessed as a 

 result of its mode of development, its surface departed from flat- 

 ness in two ways : ( 1 ) There were some minor elevations above 

 the general level, unreduced by erosion; and (2) there were 

 valleys excavated below the level of the plain. The elevations 

 were, in but few cases, more than 20 to 40 feet high ; but there 

 were occasional more considerable hills, such as Mount Holly, 

 Mount Laurel, Arneys Mount, Disbrows Hill, and the Brown- 

 town hills, the highest of which were more than 100 feet above 

 the plain on which they stood, before the deposition of the Pen- 

 sauken formation. The low mounds on the peneplain were, in 

 many places, buried by the Pensauken gravels and sands, but the 

 higher hills were not buried. Such hills as rose 40 feet or more 

 above the higher parts of the plain remained as hills after the 

 deposition of the Pensauken formation. Good examples of low 

 hills which were buried are found between Woodbury and Cross- 

 wicks, along the outcrop of one of the more resistant beds of 

 the Cretaceous system. Their crests are now at an elevation of 

 about 100 feet, and the Pensauken which once overlay them was 

 thin. 



The existence of valleys below the level of the Pensauken plain 

 is revealed by later erosion, which shows the base of the Pen- 

 sauken descending locally 40 or even 60 feet below its usual level. 

 The complete cross-sections of the valleys below the Pensauken 

 are not seen; but from the positions and relations of the low 

 remnants of the formation, it is inferred that the valleys in the 

 plain were narrow. Conspicuous examples are found at Fish 

 House on the Delaware, at Rancocas, and at Kingston, just south 

 of the Rocky Hill gorge. 



