134 CLAYS AND CLAY INDUSTRY. 



basal foot. The great bulk of the clay, however, when freshly- 

 dug, and before weathering, is black. Immediately beneath the 

 clay and forming the floor of the excavation is a layer of "iron- 

 stone" a few inches thick, beneath which occurs coarse yellow 

 sand (Pensauken). Above the clay occurs a few feet of clayey 

 loam, usually with a well-marked line of pebbles at its base. 



In the southeastern portion of the excavation a wedge-shaped 

 mass of white plastic clay of Cretaceous age was found. The 

 black clay abutted against this, and, toward the thin edge of the 

 wedge, overlay it unconformably. 1 The same white Cretaceous 

 clay is also exposed in adjoining excavations on the south at the 

 same level as the black clay, which is there absent. Above the 

 white clay occur sand and gravel deposits continuous with those 

 which overlie the black clay. The facts clearly establish the 

 recentcy of the black clay as compared to the white Cretaceous 

 clays. 



The facts, as shown in the excavations, are supplemented by 

 the records of over 50 borings, from which it appears that the 

 black clay terminates rapidly to the south, partly by abutting 

 against the underlying Cretaceous clay, and partly by thinning 

 out and giving place to gravel and sand. It extends northeast- 

 ward almost to Delair avenue, occurring on both sides of the 

 river road, but its maximum known thickness {Z 1 V 2 f ee t) is 

 apparently near the eastern portion of the present excavation. 

 Towards its limits it diminishes greatly in thickness, contains 

 lenses of sand or gravel, and is overlain by gravel which is un- 

 questionably of Pensauken age. From northeast to southwest 

 its length is about 3,800 feet, and its breadth, so far as known, 

 1,500 or 1,600 feet. It evidently occupies a somewhat circum- 

 scribed area, wherein during Pensauken submergence, unique 

 conditions (for that epoch) favorable to the deposition of clay 

 prevailed. 



Fossils. 2 — Near the base of the clay there is a bed containing 

 numerous casts of fresh-water mussels belonging to the genera 



1 That is in such a way as to show that the white clay had been eroded and 

 partly removed after it had been deposited and before the black clay was 

 formed. 



2 N. J. Geol. Surv.. Ann. Rep. for 1896, pp. 205-212. 



