JEFFERSON COUNTY. 
397 
1C9. 
1. Pleurotomaria. 2. Dellhyris expansus. 3. Pterinea orbicularis. 4. Cameroceras trentonensis (siphuncle). 
5. Ortlioceratites. 6. Orlhoceratites. 7 . Orthoceratites multilineatus. 
The orthoceratites are among the 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 Tylerville, 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. 
