INTRODUCTION. 19 



sand beds) on the supposition that the whole formation was 

 present in the type locality, but, as determined by the writer about 

 the time the term was first used in print, this is not the case, and 

 the Middle Marl cannot in the type locality be sharply separated 

 from the Lower Marl. As first used in fact the term Rancocas 

 included them both. This gave rise to somewhat misleading 

 descriptions of the Rancocas, as some features characteristic of 

 the Lower Marl were naturally ascribed to it. 



The maps published with the Report of 1868, in the region 

 southwest of Mount Holly, show four of the five above-named 

 subdivisions, which the writer differentiated in the Crosswicks 

 section. It is true that the two upper subdivisions were then 

 supposed to be the correlatives of the Red Sand and Lower Marl 

 of Monmouth County respectively, and only the two lower were 

 regarded by Cook as belonging to his "clay-marl" series. The 

 fact, however, that they had been mapped demonstrates that even 

 at that early day the distinctness of these lithologic units was 

 recognized, and it is, therefore, a little surprising that Clark 1 

 after he had mapped the entire Cretaceous belt in New Jersey, 

 decided to make only three subdivisions (Mount Laurel, Hazlet 

 and Crosswicks) in this interval, and apparently omitted from 

 his classification the Marshalltown marl bed, although it had 

 been mapped by Cook (under the term: Lower Marl )so many 

 years before. Clark refers, however, in his description of the 

 Hazlet sand, to a "well-developed dark-colored clay" frequently 

 found at its top, which would indicate that he recognized these 

 beds at some localities. 



In Cook's classification, the Middle Marl was made to include 

 a bed of calcareous sand above the greensand bed, although on 

 his early maps this lime-sand bed was represented separately 

 from the marl, but combined with his "yellow sand." The work 

 of the writer in 1894, 1895 anc ^ I ^>9^ convinced him that the lime- 

 sand bed was a lithologic unit of importance equal to that of the 

 marl bed below ( for which he at that time used the term, Horn- 

 erstown), and that this mapping was warranted. These beds 

 were, therefore, carefully traced, and the limesand was found to 

 merge. into the "yellow sand" of Monmouth County. In this 



Annual Report of the State Geologist for 1897, p. 174 et. seq. 



