Cape May Formation — Local Details. 173 



slope of about 4 feet per mile. The gradient increases toward 

 the heads of the valleys. 



At Yardville, the formation is 10 to 30 feet deep, and its 

 surface elevation is about 60 feet. Back from the stream, the 

 heavy beds of sand and gravel thin out, and the Cretaceous sur- 

 face beneath rises above this level. The materials here clearly 

 were deposited by Doctors and Crosswicks creeks. The plain 

 at 60 feet here is the topographic equivalent of the 60-foot 

 plain at Trenton, and their contemporaneity is not open to ques- 

 tion. That they are not continuous is an accident of later 

 erosion. The constitution of the formation at Yardville shows 

 that glacial materials brought down by the Delaware did not 

 go up the valley of Crosswicks Creek. The general absence of 

 silt and clay in the formation at Yardville and above indicates 

 that tributary streams were able to aggTade their valleys about 

 as rapidly as the Delaware ; otherwise the side valleys would 

 have been ponded, and deposits of silt or clay would have been 

 made. It is true that thin beds of clay appear, here and there, 

 in the Cape May formation of this and other valleys, but it 

 is exceptional. It is perhaps more common farther south than 

 in the latitude of Crosswicks Creek, and is sufficient to suggest 

 the local and temporary ponding of different streams. 



Near the Delaware the materials are gravel, sand and loam. 

 The loam is largely at the top, and glauconitic; locally it is so 

 heavy as to be used for brick. The sand, which is interstratified 

 with the gravel, is also glauconitic, more conspicuously so than 

 the loam. The gravel is mostly fine, clearly from the fine gravel 

 (pebbles the size of peas) of the Miocene, in the vicinity of 

 Stone Tavern. Back from' the streams, sand and loam pre- 

 dominate greatly over the coarser material. South of the creek 

 below Yardville, the formation is covered with glauconitic sand 

 and loam of eolian origin. Good exposures are seen southeast 

 of Yardville in the bank of Crosswicks Creek, on the road to 

 Crosswicks, and along the Allentown road. Locally there is 

 enough dune sand to modify the surface notably. It was derived 

 largely from the Cape May formation. 



