110 Belemnitella Americana and Mucronata [308 



The striking fact about both the American and European 

 occurrences is that B. americana and B. mucronata are prac- 

 tically always found in "greensand," of a very glauconitic 

 nature, or in chalk. The explanation of this rather unex- 

 pected uniformity will be discussed after a brief review of 

 the occurrences on the two continents. 



The marine Upper Cretaceous of North America is not 

 found farther north along the Atlantic coast than Long Is- 

 land where, however, only the earlier horizons are repre- 

 sented. M. L. Fuller (5, p. 77) says that well-borings are 

 sufficiently numerous to make it perfectly clear that there 

 are, on Long Island, no thick greensand beds like those in 

 New Jersey, their stratigraphic position being occupied by 

 sands. A reference to his list of Cretaceous fossils (p. 78), 

 reveals the entire absence of B. americana from all of these 

 beds. 



As noted above, the Navesink marls of New Jersey are the 

 most northern occurrence of B. americana. This member, 

 representing the middle Monmouth formations of New Jer- 

 sey and Maryland, embraces the Lower Marl Bed of Cook, 

 concerning which, W. B. Clark writes (6, p. 191): "The 

 lower Marl Bed is a characteristic greensand, glauconite en- 

 tering to a marked extent into its composition." The same 

 author (7, p. 334) writes of this formation, "The Navesink 

 marls are typically glauconitic sands. . . . The basal por- 

 tion consists generally of arenaceous beds that have been 

 hitherto referred to under the name of sand marl. Above 

 the sand marl in the northern portion of the area, is a very 

 compact blue marl, which is highly glauconitic, and fre- 

 quently fossiliferous in its central portions." 



The Monmouth formation reappears in Delaware and Mary- 

 land, where it has lost the three-fold characteristic of the 

 New Jersey section. As the beds appear in northeastern 

 Maryland and Delaware they still preserve their remarkably 

 glauconitic character. Clark (4, p. 70) says, "The Mon- 

 mouth formation consists chiefly of reddish and pinkish sands, 

 generally glauconitic, the beds in places forming a dark 



