Pensauken Formation — Local Details. 107 



material at 60 to 120 feet is similar to that at corresponding 

 elevations east of the river. That is, it is principally of arkose 

 sand, whitish to yellowish and brownish in color, with seams 

 of pebbles which develop, locally, into beds. The pebbles are on 

 the whole well worn, and many of them well rounded. Some 

 of them are disc-like. Bits of granite and shale are common, 

 and locally abundant. The sandy part of the formation has much 

 resemblance to the decomposed gneiss of the region. 



The part of the formation below 40 feet is more gravelly. 

 Sand is subordinate, and not notably arkose. Among the stony 

 materials, angular to subangular pebbles of quartz, quartzite, and 

 sandstone predominate. Bowlders and cobbles are more common 

 than at higher levels, and pieces of crystalline rock are more com- 

 mon than above. Shale occurs also, but is less well rounded than 

 at higher levels. This type of gravel has not been seen on the 

 east side of the river, and it has not been seen directly beneath 

 the normal arkose Pensauken; but its relations seem to imply 

 that it is the basal part of the valley filling, over which the Pen- 

 sauken. proper was deposited later. 



Between Rancc'Cas and Crosswicks creeks — Delaware phase. — 

 The two phases of the Pensauken are present here in the same 

 relations as farther south. The pre-Pensauken scarp separating 

 them extends from southwest to northeast through Rancocas, 

 Jacksonville, Columbus, and Mansfield, to Extonville, and is 

 essentially coincident with the outcrop of the Englishtown sand 

 (a bed of the Cretaceous), the upper part of which is more or 

 less cemented by iron. The scarp was 20 to 50 feet high at the 

 time of Pensauken deposition. The general section for the 

 region is shown in Fig. 50 (p. 136). 



Pensauken deposition here followed the lines already sketched. 

 That is, it began in the channel of the Delaware, and spread back 

 over the valley lowland to the scarp separating the Swedesboro 

 and Woodstown plains. This aggradation in the main valley 

 affected the tributaries, causing them to aggrade their valleys 

 with material brought in from the southeast. Deposition in the 

 tributary valleys appears to have kept pace with that in the main 

 valley. 



