CHAPTER IV. 



THE MERCHANTVILLE CLAY-MARL. 



The Merchantville clay-marl is a black, glauconitic, micaceous 

 clay, often somewhat sandy, the basal and upper portions of 

 the bed commonly being more glauconitic than the middle por- 

 tion. This three-fold division of the bed is usually noticeable 

 wherever a complete section of the formation can be seen. At 

 several localities the glauconitic portion of the formation is so 

 highly charged with greensand that the bed has been dug for 

 marl. 



The weathering of the Merchantville clay-marl is usually very 

 characteristic. The marly beds frequently form a more or less 

 indurated, cinnamon-brown earth in which the small black grains 

 of glauconite may be distinctly seen. When more sandy the 

 weathered portion has a peculiar "pepper and salt" aspect. In 

 the region about Jamesburg the weathered portion frequently 

 contains yellow, ferruginous, sandy nodules. In areas where 

 good sections of the formation cannot be seen, the bed can usually 

 be recognized where it is not too deeply covered with Pleistocene 

 deposits, by the rusty, cinnamon-brown color of the weathered 

 basal and upper portions of the formation. 



The contact of the Merchantville formation with the under- 

 lying beds is usually sharply defined, the upper portion of the- 

 subjacent formation usually being a loose, coarse, lignitic sand, 

 often with thin seams of black clay. Frequently an indurated 

 layer of ferruginous sandstone several inches in thickness marks 

 the exact boundary between the formations. In the northeast- 

 ern portion of the Cretaceous area of New Jersey, however, there 

 are locally heavy beds of black clay, the Cliffwood clays, near 

 the summit of the Magothy, which were at one time included by 

 Clark in his Matawan formation 1 . Later, however, the same 



1 Geol. Surv. N. J., Ann. Rep. State Geol. for 1897, p. 175, and accompanying 

 maps. 



(43) 



