CHAPTER I. 



INTRODUCTION. 



The Cretaceous formations of New Jersey occupy a belt run- 

 ning diagonally across the State in a northeast-southwest direc- 

 tion, from the shores of Raritan Bay and the Atlantic Ocean at 

 the north, to Salem County in the south, the southernmost two- 

 thirds of the belt being parallel with the Delaware River below 

 its sharp bend at Bordentown. This belt has its greatest width 

 of about 25 miles at the northeast, where it extends from Wood- 

 bridge to Asbury Park. Southeast of Trenton the width of the 

 belt is about 18 miles, but beyond Bordentown it is abruptly nar- 

 rowed and continues to the western edge of Salem County with 

 an average width of less than 10 miles. The strata slope to the 

 southwest with an average dip of about 20 feet to the mile, and 

 there are no structural features to obscure the stratigraphic 

 relations of the beds. 



The stratigraphy of this Cretaceous belt was first studied by 

 Cook, 1 who divided the entire succession of beds into three 

 series, called by him the "plastic clay" series, the "clay- 

 marl" series and the "marl" series. These three divisions 

 are practicable even to-day, but the more critical geological 

 investigations of the present time demand a more refined 

 classification of the strata than that used by Cook, especially 

 for his "clay-marl" series. Cook's classification was based 

 exclusively upon the lithologic and economic characters of the 

 beds, and since, at the time his investigations were being prose- 

 cuted, marl digging was an important industry in a, portion of 

 this Cretaciouis area, he gave far more attention to the discrimina- 

 tion of the subdivisions of the "marl" series than to those of the 

 subjacent "clay-marl" series. Cook's understanding of the 



1 Geol. N. J., 1868, pp. 241-283. 



(II) 



