GASTEEOPODA OP THE LOWER GEEEN MAELS. 21 



different kinds, and above of beds of Green Marls separated by strata of 

 lighter colored quartz sand, which are unfossiliferous. 



In the Raritan Clays, at about one-third of their thickness from the 

 base, there occurs a bed of fossil plants, prolific in genera and species, 

 which Dr, J. S. Newberry has stated to be of Cretaceous age, and at a very 

 little distance above the plant bed occur the estuary fossils above men- 

 tioned. These consist of bivalve shells, and are all of forms known to in- 

 habit brackish water, showing them to be inhabitants of an estuary or land- 

 locked bay into which fresh-water streams flowed, and making it probable 

 that there existed at the time of their deposit a body of brackish water rep- 

 resenting the present New York Harbor, but at a somewhat higher level a,s 

 compared with the surrounding land. These fossils being of estuary forms 

 and entirely of new species do not aid us materially in the determination 

 of the age of the strata in which they are found. Those already known 

 are figured and described in the previous volume, and are illustrated on 

 PI. II. They represent four different genera and five species, as follows: 



Species. 

 Genus Aatarte 1 



Genus Corbioula ., 2 



Genus Gnathodon 1 



Genus Ambonicardia 1 



The features of this latter genus, which is new to science, are more 

 nearly like some of the Jurassic forms of Europe, such as Homomya Ag., 

 than any of the known Cretaceous types either of America or of Europe. 

 No Gasteropods have yet been obtained from these beds. 



No other Molluscan remains are known to occur in these clays except 

 near the top, or perhaps in the uppermost layers. At about this horizon 

 the numerous ironstone nodules before mentioned are supposed to occur, 

 but they are always loose, having been weathered out or washed from the 

 clays, and found scattered over the surface. These nodules are well filled 

 with fossil remains of both bivalve and univalve shells, in the condition of 

 casts and impressions. They are mostly such forms as are found near the 

 base of the Lower Green Marls, or in the Crosswicks and Haddonfield 

 Micaceous Clays. 



