16 CRETACEOUS PALEONTOLOGY. 



work had been done, and he, therefore, continued his work on 

 the Cretaceous in connection with the Pleistocene mapping. The 

 chief points of difference were, first, the subdivision of Cook's 

 "clay-marl" series, for which Clark proposed the name Matawan, 

 and, second, the proper position of a bed of marl and the over- 

 lying sand in the region south of Rancocas Creek, which Cook 

 had erroneously regarded as the Lower Marl and Red Sand, 

 respectively, and in which conclusion he was at that time followed 

 by Clark. At a later period the writer was also led to differ with 

 Clark regarding the position of the so-called "yellow sand" of 

 Monmouth County. 



In the valley of Crosswicks Creek, near Walnford, the writer 

 had found a fossil bed, i to 2 feet thick, in which fossils Gryphaea 

 convexa and Belemnitella were particularly abundant. It oc- 

 curred at the base of a bed of black and chocolate marl, and at 

 the top of a loose quartz sand, and because of the contrast in the 

 adjoining beds and its induration, it 'formed a readily recogniz- 

 able horizon which could be traced for 2 miles or more along the 

 valley sides until its dip carried it below the stream bed. Prom 

 published reports, this fossil bed was inferred to mark the base 

 of the Lower Marl of Cook, and it became the starting point in 

 differentiating the lower beds. 



Between Walnford and Bordentown the "clay-marl" series of 

 Cook below the fossil layer was found to consist of five beds, as 

 follows, beginning at the top : yellow and white quartz sand, con- 

 siderably micaceous towards its base, 60-70 feet; black marly 

 clay, 40 feet ; sand with seams of clay, 30 feet ; massive clay, black 

 in deep exposures, chocolate-colored where weathered, 55 feet; 

 and a marly clay, black or greenish-black in fresh exposures and 

 weathering to a peculiar cinamon-brown porous earth, 6b feet. 

 Beneath this last bed occurred lignitic sands and clays, which 

 were regarded as a part of Cook's "plastic clay" (Raritan). 

 For a time these subdivisions were known by numbers, i to 5, 

 beginning at the bottom, but when it was found that the same 

 series of beds were repeated in each valley southwest of Cross- 

 wicks Creek the following names were substituted in 1895,* 



1 They were not used in print, however, until later. Geol. Surv. of N. J. r 

 Ann. Kept. State Geol. for 1898, pp. 3-41. 



