Pensauken Formation — Locae Detaies. 131 



Junction. Both northwest and northeast of Monmouth Junc- 

 tion its base is at about 100 feet, but toward Dayton, data from 

 wells indicate that its base is at about 90 feet. 



It appears therefore that there was a pre-Pensauken plain 

 about 5 miles wide between Jamesburg and Monmouth Junction, 

 the surface of which had little relief. This surface now has an 

 altitude 'of about 90 feet. This 90-foot lowland appears to have 

 been aggraded some 50 to 60 feet by the deposition of the Pen- 

 sauken formation. 



The area west c<f Old Bridge. — This area is but a continuation 

 of that to the southwest, nearly cut off from it by the valley of 

 a tributary to Lawrence Brook. The Pensauken formation is 

 well exposed at Old Bridge, Hardenbergh Corners, and a few 

 other points, and its disposition and relations are shown in 



Fig- 53- 



Between Rhode Hall and Old Bridge the base of the Pen- 

 sauken has an altitude of about 100 feet. At Old Bridge, the 

 uppermost 6 to 10 feet of the formation is gravelly, chiefly 

 quartz and chert, and very compact. The basal member is coarse 

 sand, slightly arkose, and having a coating of white kaolin 

 about the grains in many places. This gives the sand a singu- 

 larly white appearance. In other places the gravel and sand 

 alternate. The formation is, at a maximum, 50 to 60 feet thick 

 in this area. 



At Hardenbergh Corners a fine exposure of the formation is 

 seen in the railway cut. The basal part is coarse, with plenty of 

 crystalline rock and red shale, but the main body of the forma- 

 tion is of fine gravel and sand. A granitic bowlder a foot in 

 diameter was seen here, decayed and soft to the center. Trap 

 bowlders, one of them 3 feet in diameter, are decomposed at the 

 surface only. At this point there is a bed of coarse gravel near 

 the center of the section, with 10 to 15 feet of coarse arkose 

 sand below, and sand with but little gravel above. 



Northwest of Dunhams Corners, the Pensauken has been 

 largely removed by Beaver Dam Brook and other tributaries 

 to Lawrence Brook. Along the northwest border of that which 

 remains, its base rises locally to no feet (a mile northeast of 



