Pensauken Formation — Local Details. 91 



Local Details. 



THE LOWER DELAWARE VALLEY. 



The pre-Pensauken surface. — In pre-Pensauken time, the 

 Delaware flowed about where it is now, and received tributaries, 

 somewhat as now, from the east. Along the lower course of 

 the main stream there were two bordering plains or broad ter- 

 races. The lower plain or terrace, which will be called the 

 Swedesboro Plain, lay nearer the Delaware, and was limited at 

 the southeast by am interrupted scarp extending from Cinna- 

 minson, Merchantville, Mt. Bphraim, Woodbury, Swedesboro, 

 Auburn, through or near Halltown, to Manningiton Creek. The 

 higher plain or terrace to the southeast, the Woodstown Plain, 

 was about 50 feet higher, 3 to 5 miles wide, and was in turn 

 limited at the southeast by another scarp. These scarps were 

 determined by the outcrops of certain resistant beds of Cre- 

 taceous. The principal pre-Pensauken tributaries corresponded 

 in position, in a general way, with the present Alloway, Salem, 

 Old Mans, Raccoon, Mantua, Timber and Coopers creeks. Be- 

 low the lower terrace, the streams had rather narrow, shallow 

 valleys. 



During the Pensauken epoch, deposition was heaviest on the 

 Swedesboro Plain, and on this plain, it was greatest near the 

 Delaware. Deposition on this plain continued until it was built 

 up nearly or quite to the level of the Woodstown Plain. The 

 deposits on the lower plain contain, in most places, some arkose 

 sand and gravel which appear to be the contribution of the 

 Delaware and the Schuylkill rivers, while th.e contemporaneous 

 deposits on the Woodstown Plain were chiefly of non-arkose 

 material brought down from the east and southeast by the 

 streams coming to the Delaware from that direction. 



The existing remnants of the Pensauken are much more ex- 

 tensive on the Swedesboro Plain than on the Woodstown Plain 

 above. It was more widespread and more continuous on the 

 lower plain at the outset, and subsequent erosion has removed 



