Pensauken Formation — Description. 77 



erally covered by the Pensauken. The character of the forma- 

 tion deposited upon the marls was somewhat different from that 

 deposited upon the lower formations, nearer the axis of the 

 valley. 



In the southern part of the State, in the vicinity of Alloway, 

 an area covered by the Kirkwood had been so reduced by erosion 

 that it received the deposits of the Pensauken formation; but 

 elsewhere the northwest edge of the Miocene was above the 

 level of Pensauken aggradation. 



Except on the southeastern slope of the Coastal Plain, the 

 Pensauken does not lie on formations younger than the Kirk- 

 wood. The relations of the Pensauken on this slope will be 

 considered later. 



Relations to the youngest glacial drift. — At many places be- 

 tween Metuchen on the west and Perth Amboy on the east, the 

 drift of the last glacial epoch overlies the Pensauken formation. 

 The relations of the two show that the Pensauken was present in 

 remnants only when this drift was deposited. Valley trains 

 of gravel and sand borne out by rivers from the last ice sheet 

 were deposited in the Delaware Valley after much of the Pensau- 

 ken had been removed. Gravels of late glacial age (the Trenton 

 gravels) overlie the Pensauken at Trenton. This relation has 

 been seen repeatedly in temporary excavations, especially along 

 the Pennsylvania Railroad near Clinton Street station, and at 

 some points farther down the valley. Late glacial gravels occur 

 also in the valleys of Bound Brook and the Millstone. The glacial 

 gravel is distinct from the Pensauken in constitution; but where 

 the rivers which carried the former flowed over the latter, the 

 two types of gravel were more or less mingled in the deposits of 

 the later epoch. 



The two formations are distinct topographically in most places, 

 but in the valley of the lower Delaware, the base of the Pensau- 

 ken declines to the level of the sediments brought down the river 

 in the last glacial epoch. Where this is the case, the two forma- 

 tions are not distinct topographically, especially where only the 

 basal part of the Pensauken remains. 



