Pensauken Formation — Local Details. 121 



The valley was wide, and its southeastern slope was gentle, 

 declining from an elevation of 80 or 90 feet at Edinburgh and 

 Hamilton Square at the southeast, to 30^ feet at Bakers Basin, 

 and 10 or 20 feet at Trenton, at the northwestern edge of the 

 Cretaceous terrane. 



The upper limit of the formation northeast of Trenton is at 

 about 130 feet, along a fairly well defined line, and this appears 

 to have been its original upper limit. Northwest of the 130- 

 foot contour, the Newark shale surface rises somewhat promptly 

 to 200d= feet. There appears to have been- a somewhat definite 

 though low and gentle scarp at what is now the level of 130 

 feet, when the Pensauken gravel was deposited. Below this 

 scarp there was an ill-defined bench, whose northwestern mar- 

 gin has now an altitude of about 120 feet, and whose south- 

 eastern margin had an elevation of about 90 feet. On this 

 bench, Pensauken gravel accumulated. 



At higher levels (up to 190 or so) in this vicinity, as about 

 Ewingville and between Pennington and Lawrenceville, there 

 are cobbles and even good-sized bowlders over the surface. 

 These are interpreted as relics of an older formation, perhaps 

 the Bridgeton, which once overlay this region, but which is now 

 gone except for these relics. These bowlders and cobbles are 

 somewhat different from the coarse materials of the Pensauken. 

 Stated in other terms, the Pensauken contains certain types 

 of stony matter not known at the higher levels. 



The shale surface beneath the Pensauken north of Trenton 

 does not show valleys comparable to those of the Cretaceous 

 surface beneath the Pensauken to the southeast. The 120-foot 

 bench northeast of Trenton is probably very definitely related 

 to the 90-foot base of the Pensauken in the vicinity of Allen- 

 town, Newtown, Hamilton Square, and Edinburgh. If these 

 two levels in these localities are parts of one plain, the Cre- 

 taceous part of the plain was 5 miles wide southeast of Trenton, 

 and 8 miles wide between Princeton and Hightstown. The cor- 

 responding bench in the Newark was much narrower, 3 miles at 

 a maximum, and in some places as little as 1 mile. 



