128 Quaternary Formations oe Southern New Jersey. 



mouth Junction, the surface is generally deeply covered with 

 the Pensauken formation. Its surface elevation ranges from 

 about 70 feet at Plainsboro to about 150 feet between Prospect 

 Plains and Jamesburg, and to 170 feet south of Jamesburg, 

 where the non-arkose phase of the formation appears. Between 

 Jamesburg and Englishtown its surface is still higher. 



In the vicinity of Jamesburg, its base is at 90 feet, and the 

 formation is 30 to 50 or 60 feet thick. It is well exposed both 

 in road cuts, and in the large excavations along the railway 

 southwest of Jamesburg. Nowhere else is its composition better 

 seen. One of the striking things shown by the excavations 

 along the railway is the presence of a few bowlders up to 3 

 feet in diameter near the base of the formation. The pebbles 

 and cobbles of crystalline rock are decomposed, but the large 

 bowlders are in some cases solid except for a thin layer on the 

 outside. In the case of bowlders seen in the bottoms of pits, 

 however, a part of the weathered, decomposed exteriors may 

 have sloughed off. Red shale, ranging in size from small bits 

 to slabs a foot or so in diameter, accompanies the bits of crystal- 

 line rock. The upper part of the formation appears to have 

 been derived almost wholly from the southeast, and the non- 

 arkose phase of the formation is therefore all that is seen where 

 excavations are shallow. 



The section along the railroad exposes some 30 feet of sand 

 and gravel. The uppermost 6 to 10 feet is loamy, and rests with 

 uneven contact on the sand below. The succeeding 20 feet is 

 sand with some gravel, among which bits of granite and red 

 shale occur rarely. Gravel is subordinate to sand in some such 

 ration as 1:3. The sand is glauconitic, thin seams highly so. 

 Here and there cementation has taken place at the base of the 

 formation. Among the bowlders, sandstone and quartzite pre- 

 dominate, but one of gabbro 3 feet in diameter was seen in the 

 bottom of the pit. Its source is not known, but no formation 

 from which it could have come is known within the State. 



A mile southwest of the railway pit, a well at the 150-foot 

 level, dug to a depth of 70 feet, showed about 50 feet of non- 

 arkose Pensauken, over 10 to 15 feet of arkose material. The 

 arkose part was strikingly white, as at Old Bridge. This is one 



