SECTION I. 
CRETACEOUS GASTEROPODA OF THE LOWER MARL BEDS OF NEW 
JERSEY. 
PALEONTOLOGICAL HORIZONS OF THE MARL BEDS. 
In working over the molluscan remains described and figured in this 
and the volume on the Lamellibranchiates, I find indications of several 
distinct zoological horizons. In the first place, in the Raritan Clays, in the 
northeastern extension of them, there appears an estuary fauna represented 
by only a few species of bivalve estuary shells, but nevertheless indicating 
very clearly a fauna entirely distinct from any of those above mentioned. 
Secondly, in the clay beds near Camden, New Jersey, at Fish House, an 
entirely fresh-water fauna is found, which has yielded the twelve different 
species representing two distinct genera of the Unionide, which are described 
in the volume on Brachiopoda and Lamellibranchiata of the Raritan Clays 
and Greensand Marls of New Jersey. Above this again we have the fauna 
of the Lower Marl beds, a distinctly marine fauna, which comprises the great 
bulk of all the fossil remains known within the State. 
This bed, if properly examined, might possibly be separable into two 
zoological horizons, the lower indicated at Crosswicks Creek, near New 
Egypt, and at Haddonfield, by the dark-colored micaceous clays which lie 
at the base or, more properly, below the base of the Lower Marl bed, and 
also in the more northern portions of the State by ironstone nodules, bear- 
ing fossils usually found in the upper layers of the Raritan Clays and in 
loose pieces scattered over the surface where the upper layers of the clay 
have been denuded by the action of the weather. The fossils in these 
nodules are usually the same as those from the Crosswicks and Haddonfield 
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