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, en^bracing 

 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 



[ PAL^OKTOtOOY III.] 61 



