CLAYS OF CRETACEOUS FORMATION. 151 



the three subdivisions into which the Cretaceous in this State 

 naturally falls. The lines separating' them are more clearly de- 

 fined lithologically and stratigraphically than any others which 

 can be made, and their boundaries can be fixed in the field with 

 greater accuracy than any of the lines between the individual 

 members into which each series can be further divided. 1 



THE MARL SERIES. 



The Marl series can be divided into the following formations, 

 the essential characteristics of which are indicated by their names : 



The Upper marl (in part) . 



The Limesand [including the Yellow (quartz) sand]. 



The Middle marl (Sewell). 



The Red sand (Red Bank sand). 



The Lower marl (Navesink marl). 



Glauconite or greensand occurs in all five formations, but only 

 as sparsely disseminated grains in the two> sand members. The 

 three marl formations are composed chiefly of glauconite, with 

 small amounts of fine quartz sand and locally thin laminae of 

 clay or scattered clay pellets. These subdivisions are nearly 

 even-where readily recognizable in the field. Where their con- 

 tacts are exposed they are seen to change from one to the other 

 within reasonably narrow limits, usually 2 or 3 feet, and rarely 

 more than 6 feet, so that their boundaries are sufficiently sharply 

 marked to be accurately mapped. This definiteness is further 

 enhanced in the case of the Limesand-Middle marl contact by a 

 marked and persistent fossil bed 2 to 4 feet thick, which can 

 readily be traced across the State. 



1 Dr. W. B. Clark (Ann. Rep. State Geologist for 1897), has proposed a 

 somewhat different classification for these beds, which on lithological and strati- 

 graphical grounds seems inapplicable in several respects to New Jersey. 

 Whether or not it is the one which should finally prevail for the Cretaceous 

 of the Atlantic coastal plain is believed to be open to serious question, but this 

 point is not here considered. For the purposes of this report, the above 

 classification is more convenient, more accurate, and more readily understood 

 by the non-professional reader. 



