Pensauken Formation — Local Details. 137 



Along the old valley, the Pensauken base has an elevation of 60 

 feet or so, and on either side it is about 20 feet higher. The 

 stream in this old valley flowed to the southwest, joining the 

 Raritan valley somewhere near the lower end of the present 

 Piscataway Creek. 



Between Highland Park and Metuchen, the ragged edge of the 

 Pensauken shows much coarse gravel on the shale, left as the 

 edge of the formation was removed. The material of the Pen- 

 sauken is coarser west of Mill Brook than is its wont, and has 

 such features as to raise the question whether it is not the rem- 

 nant of a drift sheet older than that which made the well-devel- 

 oped moraine from Metuchen to Perth Amboy. 



A quarter of a mile southeast of Piscataway, at the roadside, 

 the Pensauken section is as follows : 



3) 3 feet gravelly sand with seams of red loam (doubtfully Pen- 

 sauken?) 



2) 20 feet of sand with seams of gravel. The pebbles are largely 

 quartz, but there are many red shale bits and a few granitic 

 pebbles. 



1) 7 feet coarse white arkose sand with a little gravel. 



At Bonhamtown, there is a large gravel pit exposing the for- 

 mation well. The section is not unlike that at Piscataway, and is 

 somewhat like that at Jamesburg, where 30 to 50 feet of sand 

 and gravel, chiefly from the southeast, overlie 2 to io* feet of 

 arkose gravel and sand, the two types of material being distinct. 

 At Bonhamtown, however, the arkose and non-arkose types are 

 more or less intermingled, or interbedded, or at least are not 

 sharply separated. As seen in section here, the material at a 

 given level is not arkose, while a short distance away material 

 at the same level is arkose. In no part of the section is the 

 material so free from sand of Cretaceous origin as is the basal 

 part at Jamesburg. It is clear that two different sources con- 

 tributed to the deposit at Bonhamtown, and that now one and 

 now the other made the larger contribution, while at other times 

 the two were about equal. Stratification is more distinct than at 

 Jamesburg. The sand and the gravel are commonly in nearly 

 horizontal, lens-like beds, a few inches thick. The gravel is 



