CHAPTER IX. 



THE MOUNT LAUREL-NAVESINK 

 FORMATIONS. 



In the bluff at Atlantic Highlands the Mount Laurel formation 

 includes from 3 to 5 feet of quartz sand, with some glauconite, 

 the "sand marl" of Cook, and has afforded an abundance of fos- 

 sils. Immediately. above this bed at the same locality there are 

 10 or II feet of typical, nearly pure greensand, the Navesink 

 marl, although the entire Navesink formation is not exposed here, 

 its total thickness in the region of its typical development in east- 

 ern Monmouth County being about 30 feet. In the region where 

 it is typically developed the Navesjnk marl is sharply defined 

 below, but towards its surrtait it gradually passes into a layer of 

 darker color, with less glauconite and with more sandy clay, 

 sometimes micaceous, the transition to the superjacent Red Bank 

 sand being somewhat gradual. About 10 feet from the base of 

 the Navesink, in eastern Monmouth County, a conspicuous shell 

 layer about one foot in thickness and composed almost entirely 

 of the shells of Gryphaea convexa is a very constant feature of the 

 formation. 



In the southwestern extension of the Mount Laurel and Nave- 

 sink formations the lower sand formation apparently increases in 

 thickness at the expense of the upper greensand marl formation, 

 until it is probable that the entire interval occupied in eastern 

 MonmOiUth County by the twO' formations is occupied by the 

 Mount Laurel sand alone. 



FAUNA OF THE MOUNT LAUREI^-NAVESINK FORMATIONS. 



The faunas of the Mount Laurel sand and the Navesink marl 

 constitute a single unit, and in any discussion of them they must 

 be considered together. Collections of this fauna have been made 



(103) 



