50 TKANSACTIONS OF THE [1889 



view of the beds along both dip and strike. The exposure here 

 is more sandy above than in the preceding one, and diifers from 

 it in having a drift of quartz pebbles at base. Towards the 

 east this stratum of pebbles is close, only a few inches thick, but 

 it widens westward, and is continued by having the pebbles shot 

 wide apart until it terminates a few rods down the creek. The 

 Black Marl is here just the same, and of about the same thick- 

 ness as in the other exposure, but it is much richer in casts of 

 fossil shells, and these occur without the least regularity in 

 nearly all parts of the bed. Above this rests the clay-like 

 greensand marl, as before, which soon becomes ferruginated 

 above, loses its glauconite, and assumes a looser and more sandy 

 character. Over this rests the red sand, and on top of all is a 

 Quaternary yellowish sand and loam, with less gravel than 

 farther west. 



One stage farther back, at a higher level, vestiges of the 

 Eocene shell-marl appear in a deep cut of the surface, but no 

 considerable bed of that material is seen in place. But at a 

 distance of about one-eighth of a mile from the second bare clifF, 

 up the Piscataway, a very extensive exposure of the Eocene shell- 

 marl forms a bold boundary of the inner side of a wide cove which 

 has been eroded from the continuation of the Fort Washington 

 ridge. This series of fossiliferous beds rests apparently at a level 

 of about fifty feet above the water of the creek, but its exact base 

 cannot be explored because of the thick body of fallen material by 

 which it is covered. This exposure will be more fully described 

 in connection with the Eocene formation. 



On the eastern side of this wide cove the black plastic clay 

 of the Lower Marl bed makes an appearance from a few feet 

 above water level, but at a distance of more than fifty feet from 

 the low bank of the Piscataway. As before, the low terrace is 

 composed of the downthrow of materials from the adjoining 

 hills, but here it is chiefly built of soft and fine materials 

 which have been spread out by the activities of a tributary 

 brook. This alluvial material rests directly upon a shallow 

 exposure of the Baltimorean variegated clay, and takes the 

 position which formerly must have been occupied by the Albi- 

 rupean and Cretaceous strata as they appear in the sections 



