The Rensselaria ovoides is a much larger and more 
handsome brachiopod than any of the others. It is only 
occasionally found. 
Among Gasteropods we have found a large Platyceras 
nodosum, and a smaller univalve, the Flatyostoma ven- 
tricosa. 
Economic Vatuse. In some places the sand has been 
used for manufacturing glass. It is also reported that 
when the Erie Canal was constructed that blocks of the 
Oriskany Sandstone were used in the locks at Jordan, and 
it is said to have worn very well for a rock of that charac- 
ter. Inasmuch as iron exists quite plentifully in the rock, 
quantities of it have frequently been obtained for the pur- 
pose of smelting. Nevertheless the difficulties of extrac- 
tion, together with the attendant expense, have heretofore 
proved insurmountable obstacles to a successful enterprise. 
CORNIFEROUS PERIOD. 
In nearly all the places where we found the Oriskany 
Sandstone it was overlaid by a very tough limestone. 
This protected it, not only from such destructive agen- 
cies as air, frost and moisture, but also from the attacks 
of enthusiastic geologists, who might otherwise have soon 
appropriated our small allowance of that interesting 
period. 
The limestone is the last of the great limestone forma- 
tions, the Corniferous. It has sometimes been called the 
Upper Helderberg Group to distinguish it from the Lower. 
It is found very abundantly in our county, and is chiefly 
a limestone formation. The period has been divided into 
three groups: the Schoharie Grit, Caudi-Gauli Grit and 
the Corniferous Limestone. Only the last of these is 
found in our county. This has usually been subdivided 
into three divisions, the Onondaga, the Corniferous, and 
the Seneca Limestones. Although these divisions are all 
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