148 
GEOLOGY OF THE FOURTH DISTRICT. 
It is not everywhere the purely siliceous sandstone which appears in the western part of 
the State. At Schoharie and in the Helderberg generally, it is a siliceous limestone, very com¬ 
pact and tough where penetrated beyond the influences of the weather; but very rough and 
with numerous cavities upon the exposed surface. It received the name of Shell grit from 
Prof. Eaton, from the abundance of its fossils and its siliceous character. 
Organic remains of the Oriskany Sandstone. 
I lie most obvious of the fossils of this rock are figured in the following woodcut from Mr 
Vanuxem’s Report: 
59. 
1. Deltliyris arenosa. 2. Atrvpa elongata, 3. Atrypa peculiaris. 
1. Deltliyris arenosa (Conrad, Geol. Report , 1839, p. 65.) Shell semi-oval, depressed 
in front; extremities of the hinge line rounded ; surface marked by about sixteen or eighteen 
flat ribs on each side the mesial fold, and four or five on the fold : ribs, particularly near the 
margin of the shell, crossed by elevated undulating lamellae or lines of growth ; beak in¬ 
curved ; area rather large. 
2. Atrypa elongata (Conrad, Geol. Report , 1839, p. 65.) Shell ovoid, crossed by nu¬ 
merous sharp radii, which extend from the beak to the base and sides ; lower valve gibbous 
in the middle, with an elevated ridge extending from beak to base ; lateral margins often 
straight. 
This is an exceedingly abundant fossil, the radii often becoming obsolete towards the beaks. 
It is often less contracted at the base than the figure. 
