152 CLAYS AND CLAY INDUSTRY. 



The only exceptions to the above statement regarding the 

 sharpness of contact are these. First, the top of the Upper marl 

 (Cretaceous) passes into the Eocene marl without a break and 

 with but little lithological change. The fossils, however, are 

 decisive as to the age of the beds, although the division between 

 the two formations can be made with difficulty in the field. Sec- 

 ond, in Burlington, Camden, Gloucester and Salem counties, the 

 Red sand, which separates the Lower from the Middle marl, is 

 apparently absent, due to thinning out in the vicinity of Sykes- 

 ville, Burlington county. The Middle marl is, therefore, in these 

 counties superimposed upon the Lower marl, and it is impos- 

 sible except in a general way to differentiate them. This is par- 

 ticularly the case the farther one passes southwest beyond the 

 point of disappearance of the Red sand. 



The location of the Marl series is shown in a general way on 

 Plate X, where it lies immediately northwest of the line indicating 

 the boundary of the Miocene. It extends in an ever-narrowing 

 belt from Atlantic Highlands and Long Branch at the northeast, 

 in Monmouth county, to Salem', Salem county, at the southwest. 

 The narrowing outcrop to the southwest is due in part to a 

 lesser thickness consequent on the disappearance o<f the Red sand, 

 but more particularly to the overlap of the Miocene sands and 

 clays. In the southwest these rest upon the Middle marl, save 

 where the larger streams have eroded them back and exposed 

 the Lime sand. In eastern Monmouth county, on the contrary, 

 the Miocene rests upon the Eocene marls, and the whole of the 

 Cretaceous marl series is exposed. Since the Marl series con- 

 tains no beds of workable clay, it will not be further considered. 



THE CLAY MARL SERIES. 



The Clay Marl series includes beds of sand, marl, and clay 

 which underlie the Marl series, described above, and overlie the 

 Raritan or Clay series. Its base is marked by the contact of a 

 black, glauconitic sandy clay upon a cross-bedded lignitic sand, 

 containing laminae and lenses of black, nonglauconitic, micaceous 

 clay. The glauconitic clay at the base of the Clay Marl series 

 weathers into a verv characteristic cinnamon-brown, indurated 



