CHAPTER X. 



THE RED BANK SAND. 



The Red Bank sand, the "red sand" of Cook, has its most 

 characteristic development in eastern Monmouth County. In the 

 lower beds of the formation there is a gradual transition from 

 the subjacent Navesink marl, from lo to 20 feet of the lower 

 beds being dark-colored sandy clays, with more or less glau- 

 conite. The great mass of the formation, at least in the weath- 

 ered condition in which it is usually seen, is composed of a highly 

 characteristic, very ferruginous red sand. The total thickness of 

 the formation in eastern Monmouth County is nearly 100 feet. 



Towards the southwest the Red Bank sand becomes much less 

 characteristic, the bed being reduced in thickness, until beyond 

 the western border of Monmouth County the formation cannot 

 be differentiated. It has already been shown how the Navesink 

 marl of eastern Monmouth County is displaced in its southward 

 extension by the greater and greater development of the sub- 

 jacent Mount Laurel sand. It is undoubtedly true that the 

 Belemnitella fauna of the Mount Laurel-Navesink represents a 

 contemporaneous life zone, and consequently the boundary line 

 between the Mount Laurel and Navesink is not a contempo- 

 raneous line, but in passing from the northeast to the southwest 

 represents a later and later time until finally the sand deposition 

 continues through the entire period of deposition of the Nave- 

 sink marl of eastern Monmouth County, and the g'reensand 

 deposition becomes contemporaneous with the typical Red Bank 

 sand of the more northeastern area, and continues without in- 

 terruption into the Hornerstown marl formation. The disappear- 

 ance of the Red Bank sand to the southwest, therefore, does not 

 represent any lack of continuity of sedimentation, nor an over- 

 lap unconformity, but simply a change in the nature and thick- 

 ness of the sediments in passing along the strike of the beds. 



(137) 



