JEFFERSON COUNTY. 

 109. 



397 



1. Plcurotomaha. 



2. Deltliyris cxpansiis. 3. Pterinea orbicularis. 4, Camcroceras trcntonensis (sipliuncle). 

 5. Ortlioccraliles. G. Orllioceralitcs. 7. Ortiioceratites uiullilineatus. 



The orthoceratitcs are among tlic oldest genera of the animal kingdom. I observed in the 

 calciferous one large species, but it may be considered rare in this rock. In the birdseye, 

 however, as has been observed, they are among some of the largest fossil bodies of the kind. 

 In the trenton, the individuals of some species are quite numerous, but no more so than in 

 former or subsequent periods in the New-York rocks. 



Utica Slate. 



It is a remarkable fact, that this rock, which succeeds the trenton limestone, and which is 

 lithologically constituted like the slaty part of the trenton, should still, among its most impor- 

 tant characters, possess those which are so diverse. The facts in these respects will appear 

 in the subsequent pages. 



I have already had occasion to remark, that this rock is quite limited in this county, notwith- 

 standing it is well developed. Its outcrop may be traced from near Adams, in a curvilinear 

 line, to two miles north of Whitesville and Tylcrville, where it passes round eastwardly beyond 

 the limit of Jefferson. The belt or area exposed is rarely more than two or three miles wide. 

 Towards the southwest, it disappears beneath the loraine shales. It is also exposed in the 

 great gorges in Rodman and Loraine, the great mass of shales being cut through by the 

 sandy creeks. 



