ORISKANY SANDSTONE. 
The Oriskany sandstone everywhere succeeds to the upper members of 
the Lower Helderberg group, and, at several points, extends beyond 
the known geographical limits of the latter. In the greater number of 
localities within the State of New-York, the transition from the upper 
calcareous beds of one group to the siliceous or sandy beds of the other 
is very abrupt; while in other instances there is an intermingling of 
calcareous matter in the lower beds of the sandstone. In these instances, 
however, as well as in others, the siliceous material appears to have been 
to a considerable degree in the condition of gelatinous silex, producing a 
rock approaching in character to hornstone; while other examples present 
an appearance as if the grains of silex had been softened, or agglutinated 
by a siliceous paste. In its more fossiliferous parts the rock is a mixture 
of silica and carbonate of lime ; and the action of the weather, dissolving 
and removing the latter, leaves a grayish brown porous mass, embracing 
the casts of the interior and moulds of the exterior of the fossil shells. 
In many places the rock consists of a sandstone of nearly pure white, or 
graduating from white to buff-colored : in more southern localities, it 
often presents the aspect of a siliceous limestone, not differing greatly 
from the succeeding limestones. 
While in the State of New-York the accessible portions of the rock 
furnish us for the most part with casts of its fossils, or, if beyond the 
reach of weathering, with a compact mass of calcareous sandstone in 
which the fossil remains are closely imbedded, we find, in Maryland and 
[ Palaeontology III.] 51 
