GASTEROPODA OF THE LOWER GREEN MARLS. 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. 8. 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 as 
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 yolume, and are illustrated on 
Plu. They represent four different genera and five species, as follows: 
Species. 
Genus Astarte... 22. 22.2 ek eee ce een ce ene ce ene cee ee conn cee ns cee cee ceeees 1 
Genus Corbicula ..2-2. 0.0 o ee eee ne ce ee cn nee cw eee cece nn cece ns cen ees ceeees 2 
Genus Gnathodon ... 22. oe eee ene ce en tees cece e ccc ne cee nes coeees 1 
Genus Ambonicardia ...... 22.2... cece cece eee ce ces ween ee cece ee cece wees 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. hey are mostly such forms as are found near the 
base of the Lower Green Marls, or in the Crosswicks and Haddonfield 
Micaceous Clays. 
