150 CLAYS AND CLAY INDUSTRY. 



The Cretaceous formations ini New Jersey can be naturally 

 grouped into three series, a glauconite Marl series at the top, a 

 Clay series at the base, and a Clay Marl series in the middle. The 

 Marl series and the Clay Marl series belong to the Upper Cre- 

 taceous; the Clay series to the Lower Cretaceous. 



As is implied by the above names, each of these series is char- 

 acterized by certain deposits of economic importance. The Marl 

 series contains valuable beds of glauconite or greensand marl,, 

 which were very extensively dug for fertilizer in former years, 

 and which are still in use to a more limited extent. The Clay 

 series contains important beds of clay, some of great value. The 

 Clay Marl series contains beds of clay and beds of marl, both of 

 which have been utilized economically; but the clays are not so 

 good as the best of those in the Clay series beneath, and the 

 marls are inferior to the greensands of the Marl series. No marl 

 occurs in the Clay series, nor has any workable clay been found 

 in the Marl series. 



Although the three divisions of the Cretaceous can thus be 

 divided into> a Marl, a Clay Marl and a Clay series, it must not 

 be supposed that these divisions are composed exclusively of 

 marl, clay marl and clay. This is far from the case. In each 

 series there are several thick beds of sand, which make up prob- 

 ably more than half of each series. The Marl series is them a 

 succession of interbedded layers of marl and sand ; the Clay 

 series, of clay and sand; the Clay Marl series-, of more or less 

 glauconitic clays, glauconitic sands and marls. In the case of 

 the Marl series and of the Clay Marl series, these subdivisions are 

 so distinctive, and so sharply marked from each other, and hold 

 their characteristics so continuously, that they can be nearly all 

 traced without difficulty across the State, and their limits ac- 

 curately defined on a map. In the case of the Clay series, how- 

 ever, there is less regularity, and only in a comparatively narrow 

 area between Wloodbridge and South Amboy, where the beds 

 have been exposed in many large openings, can definite horizons 

 be made out and traced beyond the limits of individual exposures. 



The three major subdivisions here outlined are the ones best 

 suited to bring out the lithological and economic characteristics 

 of the Cretaceous system in New Jersey. They are, moreover, 



