74 Quaternary Formations of Southern New Jersey. 



The present elevation of the pre-Pensauken plain of erosion, 

 that is the plain on which the Pensauken was deposited, is great- 

 est at the northeast and decreases to the southwest. Along the 

 axis of the valley, the base of the formation has an elevation of 

 about ioo feet between South Amboy and Philadelphia, about 

 60 feet in the vicinity of Swedesboro, and 30 to 40 feet in the 

 vicinity of Salem. East and south of the axis of the valley, the 

 pre-Pensauken plain is somewhat higher. In the lower Dela- 

 ware region, there seems to have been a rude but broad terrace 

 east of the main valley plain, 30 to 50 feet above it. The Pen- 

 sauken aggraded the lower plain to the level of this terrace, and 

 spread out upon it in places at least. Locally, the base of the 

 formation is considerably lower than would be indicated by the 

 figures given above. In these places it appears to have filled 

 narrow gorges below the level of the broad valley. 



The altitude of the Pensauken surface. — The surfaces of rem- 

 nants of the Pensauken formation are not, in all cases, to be 

 taken as representing its original surface. In the vicinity of 

 Salem and Alio way, the surfaces of Pensauken remnants have 

 an altitude of 65 to 90 feet; about Auburn, 80 to 90 feet; at 

 Swedesboro', 80 to 100 feet; at Haddonfield and Philadelphia, 

 about 120 feet; at Rancocas, 90 feet; at Deacons Station, no 

 feet; at Bordentown, 120 feet; at Trenton and Kingston, 120 

 to 130 feet; at Griggstown, 150 feet; at Allentown, 150 feet; 

 southeast of Hightstown, at Englishtown, Hazlet, and South 

 Amboy, 170 to 180 feet; and at Metuehen, about 130 feet. 

 These heights vary much, but only the surfaces of the larger 

 areas can be presumed to represent approximately the original 

 surface of deposition. At the time of its deposition, the surface 

 of the formation probably was lower than now. 



If the elevations of the larger remnants mentioned above be 

 taken as representing remnants of the original surface of deposi- 

 tion, and if the eroded beds of the formation were restored, the 

 Pensauken surface would decline gradually to the south west 

 from an area about Hightstown and Englishtown, and from the 

 same locality there would be a very slight decline to the north- 

 east. Aside from these gentle slopes, minor slopes in various 



