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 
Mollusea 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 Ostreid@ and Spondylide 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, Gryphea vesicularis, and two species of naticoid shells being 
all that are yet known to pass into it from below; even the Gryphea 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, Gryphea 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 occurs a series of beds of consider- 
able thickness in which no molluscan 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 fauna entirely distinct from that of either of the beds below, 
being composed not only of different species, but largely of different genera, 
