SECTION I. 



CBBTACEOUS GASTEROPODA OF THE LOWER MARL BEDS OF NEW 



JERSEY. 



PALEONTOLOGICAL HORIZONS OF THE MARL BEDS. 



In working over the moUuscan 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 Unionidce, 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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