Pensauken Formation — Description. 87 



the northwestern border there is much shale in the Pensauken, 

 at least in spots. This is true, for instance, northeast of Trenton. 

 Southeast of Trenton, where the. underlying formation is schist, 

 much material from this formation appears in the gravel. On 

 the other hand, the correspondence between the composition of 

 the younger formation and the character of the base on which 

 it rests, or of the older rocks against which it abuts, is not so 

 close as the shore hypothesis seems to demand. Shaly material 

 is found in spots, at least, far from the outcrops of the shale, 

 and on the opposite side of the hypothetical sound. 



The arkose character of the sand is well developed from 

 Trenton to Wilmington near the Delaware, about Hamilton 

 Square, Newtown, Hightstown, South Amboy, Old Bridge, and 

 Woodbridge. From both the northeast and southwest, the arkose 

 character becomes less conspicuous towards Jamesburg, where 

 much of the formation seems to have come from the south. 

 This suggests that the Delaware and the Hudson were the great 

 contributors of the arkose sands, and that at Jamesburg, about 

 equally distant from the two sources, it is least prominent. 



Theoretically the Raritan was equally well situated for bring- 

 ing in arkose Pensauken gravel, but in that part of its former 

 basin which is low- enough to have received deposits, remnants 

 of the Pensauken are small. 



There is nothing in its constitution to negative the hypothesis 

 of the whole formation being river work, nor is there any- 

 thing, as now understood, to prove it. The widespread uniform- 

 ity of the second number (p. 81) might be said to argue sub- 

 mergence. The upper member, on the other hand, is more like 

 flood plain deposits, or subaerial wash. The basal member, also, 

 is not unlike a river deposit, though it is difficult to understand 

 how such coarse material could have been carried by rivers so 

 far with so little rounding. The help of floating ice seems to 

 afford the only escapefrom the difficulty. 



The absence of fossils in all places where the formation is 

 normally developed, is negative evidence. The condition of the 

 formation in most places is such that fossils could not have been 

 preserved, even had they been abundant at the outset. At Fish 



