CLAYS OF CRETACEOUS FORMATION. 183 



tion. Its importance is due to its great thickness (50 to 80 feet 

 where not eroded) , to its wide outcrop, and to' its character. 



It has been opened in four somewhat distinct areas;, a) south of 

 Woodbridge, b) north of the Raritan river from Florida Groive 

 to Bonhamtown. c) south of the Raritan from South Amboy to 

 Sayreville and south to Jas. Bissetts' brickyard on South river, 

 d) at South River village and west to Milltown. The four dis- 

 tricts may be spoken of briefly as a) the Woodbridge area, b) the 

 Sand Hills area, c) the Sayreville area, d) South River area. The 

 Woodbridge and Sand Hills areas are separated from each other 

 by a belt of hills, the tops of which are formed either by thick de- 

 posits of glacial drift or by the higher members of the Raritan 

 formation, i. c, the "Feldspar-Kaolin" sands, and the South Am- 

 boy fire clay. Whether or not the Woodbridge clays are contin- 

 uous across the belt beneath these later deposits, or whether the 

 core of the ridge of hills is formed by the Triassic red shale, as 

 may be inferred from an isolated knoll of this formation between 

 Eagleswood and Spa Spring is uncertain, The Sayreville and 

 South River areas are separated from each other, and from the 

 other two by the deep trenches of the Raritan river and of its 

 tributary, South river. The clay bed was beyond a doubt formerly 

 continuous between them, but the excavation o<{ the river valleys 

 has dissected it and removed a large part of the clay, so that, al- 

 though these rivers, by affording navigable waterways and cheap 

 means of transportation, have greatly enhanced the value of the 

 clays along their valleys, yet their existence has been accomplished 

 by the erosion and removal of much of the clay stratum. 



Thickness. — The thickness of this member varies from; about 

 50 feet in the vicinity of Woodbridge to> 80 feet near Spa Spring 

 and Maurer, as shown by borings, but this amount of clay is 

 nowhere exposed in any one bank. At many of the banks near 

 Woodbridge, particularly the more northwesterly openings, the 

 upper part of the bed has been eroded away, and only the lower 15 

 or 20 feet remain. In fact, there has. been a varying amount of 

 erosion wherever the yellow Pensauken gravel or the red glacial 

 drift lies upon the clay (Plate XXI, Fig. 1). In some cases also 

 huge masses of the clay many feet in diameter have been included 

 in the drift, as in Plate XXI, Fig. 2. But where the black, lam- 



