ORISKANY SANDSTONE. 4©3 
Among the Lamellibranchiata we have a few aviculoid forms, which, 
except in their size, form no marked contrast with those which preceded 
or those which follow. 
In the Gasteropoda, I have already shown* that the Genus Platyostoma, 
in its typical species, occurs both in the Lower Helderberg rocks and in 
the Oriskany sandstone, while it is also known in the higher formations. 
The Strophostylus is equally characteristic of the Lower Helderberg 
limestones and of the Oriskany sandstone, though at present not well 
determined in the higher formations. The Platyceras, in several formsj 
is quite abundant in the Oriskany sandstone ; two or more of the species 
being common to this rock and to the Lower Helderberg limestones. We 
have likewise the casts of two spiniferous species in this rock, showing 
their affinities with those of the Upper Helderberg limestones. 
It is not possible, therefore, to point out any changes in the fauna of 
this period sufficient to indicate the commencement of a new system, 
and its relations with the formations below are as intimate as with those 
above ; while in the Northern and Middle States, the Oriskany sandstone 
bears in its fauna a closer relation to the lower than to the overlying 
formations. It is, moreover, in the State of New-York, separated from 
the succeeding fossiliferous rocks of the Upper Helderberg group by the 
non-fossiliferous or almost non-fossiliferous belt of the Cauda-galli grit* 
which often attains a thickness of one hundred to one hundred and fifty 
feet. 
The order is as follows : 
Schoharie grit i Lowest member of the Upper Delderberg group; 
Cauda-galli griU? i Non-fossiliferotis; 
Oriskany sandstone. 
Upper Pentamerus limestone i Highest member of the Lower Uelderjberg group. 
It may be regarded that the physical conditions which inaugurated the 
Oriskany sandstone prevailed through the period of the Cauda-galli grit, 
disappearing in the Schoharie grit and succeeding limestones. It is not 
* See page 308 of this .volume. 
