Pensauken Formation — Locae Details. 133 



Between Fresh Ponds and Dayton is the great Pigeon Swamp, 

 which occupies a broad flat valley. Its altitude is about 80 feet, 

 and its borders on the north and south about 20 feet higher. 

 Exposures of the material beneath the swamp are mostly want- 

 ing; but some information was afforded by a drainage ditch 

 through the marsh some years since. This ditch reached Cre- 

 taceous clay but a few feet below the surface, and at the west end 

 of the swamp Cretaceous beds rise as high as 70 to 80 feet. The 

 Pensauken appears to have been mostly removed from the area 

 where the swamp is. The stream now flowing through it is small, 

 and apparently inadequate for the work of erosion which seems 

 to have been accomplished. The swamp is quite unlike the valleys 

 of other tributaries to Lawrence Brook, for the others seem 

 capable of having made the valleys they occupy. 



Southeast of Pigeon Swamp there is a broad depression, a mile 

 southwest of Rhode Hall, at about 90 feet. It is three-fourths of 

 a mile wide, and opens out into the valley of Manalapan Creek 

 to the southeast. It seems possible that Manalapan Creek flowed 

 through this gap in post-Pensauken time, going on northwest 

 through what is now Pigeon Swamp, to Lawrence Brook. The 

 valley of South River, between Jamesburg and Old Bridge, is 

 probably following a course assumed in post-Pensauken time. 



The early post-Pensauken drainage may have been somewhat 

 as follows : 1 ) A stream flowing northwest from Wickatunk 

 to Old Bridge, joining the Raritan in the vicinity of Sayreville; 



2) Manalapan Creek, flowing northwest from Manalapan to 

 Jamesburg, and thence to Lawrence Brook at Deans Station; 



3) Lawrence Brook, flowing to the Raritan in a valley in the 

 Pensauken formation, overlying Newark shale. The first of 

 these three streams excavated its valley faster than the last. After 

 it had been sunk through the Pensauken into the Raritan forma- 

 tion, it had great advantage over Lawrence Brook after the latter 

 reached the Newark shale. It is conjectured that a tributary to 

 the Old Bridge-Sayreville stream developed southwest from Old 

 Bridge until it tapped Manalapan Creek in the vicinity of James- 

 burg and led it off to its main, now South River. This diversion 

 of Manalapan Creek left the gap southwest of Rhode Hall un- 



