22 PALEONTOLOGY OF NEW JERSEY. 



The next zoological horizon is that of the Lower Green Marls proper, 

 in which are found by far the most of the Cretaceous fossils yet recognized 

 within the State. The number of species so far exceed those of any of the 

 other beds named above as scarcely to bear comparison, the number of 

 MoUusca alone being 303 species out of a total for all formations of 441. 

 These fossils are, however, like those of the other beds, found mostly in the 

 condition of internal casts, or casts representing partially the interior cav- 

 ity, but they also carry on them the imprint of the external markings to a 

 partial extent. Very few of the specimens preserve even a replacement of 

 the original substance. The Ostreidce and Spondylidee are notable exceptions 

 to this rule, being generally found with the substance of the shell entirely 

 preserved, but so friable as to be easily destroyed after collection. In the 

 Micaceous Clays of the Crosswicks Creek and Haddonfield beds, however, 

 the substance of the shells is entirely preserved, both of bivalve and uni- 

 valve species. 



In the Middle Marls, a fauna almost entirely distinct from that below 

 presents itself, Gryphcea vesieularis, and two species of naticoid shells being 

 all that are yet known to pass into it from below; even the Gryphcea is 

 here presented under a varietal form not common in the Lower Marls. In 

 this bed some of the species are represented by great numbers of individ- 

 uals, the Teredo, Gryphcea and Terebratula being the most abundant. 



At the base of the Upper Marls another entirely distinct fauna is found, 

 still presenting Cretaceous features. In this layer also few species are rep- 

 resented, and, so far as I am aware, no locality has yet been found where 

 they occur in any abundance; and no species have yet been observed in 

 it that are common to either of the others below. Above this fossiliferous 

 layer at the base of the Upper Marls occm-s a series of beds of consider- 

 able thickness in which no moUuscan remains have been detected. Many 

 vertebrate fossils have been discovered, however, showing a quite remark- 

 able break in the molluscan life in the seas of the New Jersey area, 

 extending to the top of the Upper Marls, where occurs the Eocene layer. 

 This contains a faima entirely distinct from that of either of the beds below, 

 being composed not only of different species, but largely of different genera, 



