134 Quaternary Formations of Southern New Jersey. 



occupied by a stream, and the valley of the beheaded part of the 

 former Manalapan Creek became swampy (Pigeon Swamp), as 

 a result of the sluggish drainage which resulted from the lessened 

 flow. 



Deposits between Lawrence Brook and the Raritan River. — 

 North of Lawrence Brook the Pensauken formation occurs most 

 of the way from Deans to New Brunswick, the Pennsylvania Rail- 

 road marking, in a general way, its northwestern limit. Its sur- 

 face here has an elevation of from about ioo feet to 125 feet. At 

 New Brunswick its base has an elevation of about no to 120 

 feet, but it declines to about 70 feet at Westons Mills. 



The formation here is somewhat drift-like in composition, 

 containing much coarse material of northern origin. It lacks 

 evident stratification in places, especially in the railway cuts 

 between New Brunswick and Milltown, at 1 10 to 120 feet. The 

 material here is very unlike that at Milltown and southeast of 

 Lawrence Brook, and has somewhat the appearance of glacial 

 drift. In many places the gravel is associated with a good 

 deal of clay from the Newark shale, emphasizing its drift-like 

 aspect. The hypothesis has been entertained that the ice at 

 some time reached this latitude, but proof of its truth is wanting. 



South and west of New Brunswick (Voorhees, Clyde, and 

 Middlebush) are scattered bits, but not considerable beds of 

 Pensauken material. Large tracts here which are at levels ap- 

 propriate for the formation are without it, and the reason for 

 its absence is not altogether clear. (1) Was the New Bruns- 

 wick region built up to 160 feet, the Old Bridge level, and since 

 lowered by erosion, or (2) was this region too high in Pensauken 

 time, for the deposition of that formation? In either case there 

 has been much erosion since. A third alternative is that the 

 Old Bridge-Amboy region has been raised a little, relative to 

 the New Brunswick region, since the Pensauken epoch. Which, 

 if any, of these conjectures is correct, is undetermined. 



One and one-half miles west of Franklin Park, and 2^ miles 

 east of Griggstown, the 150-foot hill has a cap of 10 feet or so 

 of gravel. A mile north of west of this, the 140-foot hill has 

 a gravel cap very like the gravel and sand about New Bruns- 



