ifesozoic and Comozoic Geology and Paloeontolocjy. 49 



remarkable purit3\ Among these occur beds of pure potter's clay. 

 This division of the general series rests along its northwest margin, 

 from the Raritan to the Assnnpink, in an unconfoimable manner upon 

 the middle secondary rocks, and from the Shipetaukiu to the Delaware, 

 upon the upturned strata of the primar,y belt. It contains, toward its 

 iipper beds, much of the dark blue sandy clay, which is also associated 

 with the overlying grcensand, from which it is not separated by any 

 well-defined limit. 



Second. — A somewhat mixed group, consisting of beds almost 

 wholly composed of greensand, in a loose and granular condition, al- 

 ternating with and occasionalh' replaced by layers of a blue, sandy, 

 micaceous cla3^ This is the " greensand formation," properly so 

 called. Having been used, however, for agricultural purposes, it has 

 acquired the name of marl. It comprises, strictly speaking, several 

 subordinate beds, all belonging, however, to two principal varieties. 

 In the first of these, the green, granular mineral is the predominant 

 and characteristic ingredient. The second consists, on the other 

 hand, of a dark-blue clay, mingled with more or less silicious sand. 

 This latter material constitutes the usual floor upon which the true 

 greensand deposit rests ; and it occurs, in like manner, especially in 

 the northern and eastern portions of Monmouth county, both above 

 the uppermost visible greensand, and included between its beds in one 

 or more alternations. 



Third. — Immediately overljMng the greensand formation near its 

 southeastern border, there are several limited exposures of a yellowish 

 granular limestone, of rather crystalline structure, and frequently sili- 

 cious composition. This rock' exists in rather irregular, thin, flaggy 

 bands, usually from one to three inches thick. Between these there 

 are often thin layers of loose, granular, calcareous sand, identical, or 

 nearl}^ so, with the matter of the rock, but destitute of cohesion. This 

 formation contains a profusion of organic remains, many of which be- 

 long in like manner to the underlying greensand, though some occur 

 in it alone. Eesting usually in direct contact with the greensand 

 stratum, it contains often a moderate proportion of the green granular 

 mineral, sprinkled throughout its mass. It is useful as a source of 

 lime in a district where there is no other calcareous stratum. 



Fourth. — A yellow, very ferruginous, coarse sand, containing some- 

 times a small proportion of the green mineral. This stratum is in 

 some places thirty feet thick. In the Nevesink Hills, and in one or 

 two other localities, it occurs as a soft sandstone, containing hollow 

 casts of fossil shells. Throughout much of the central portion of the 



