146 



GEOLOGY OF THE THIRD DISTRICT. 



LUt of Fossils from the Reports, etc. of T. A. Conrad, identified and named tip to this 

 period, which are found in the Comiferous limestone. 



Delthyris acuminata. 

 Strophomena undulosa. 

 — rugosa. 



TssTACEA, OR Shells. 



Platyceras diunosum, fonnerly Pileopsis tubifer. 

 Cyitoceras trivolvis. 

 — matheru 



Crustacea. 

 Odontocephalus selenurus. 



21. MARCELLUS SHALES. 



Commencement of the Pyritiferoua Rock {or Third Greywacke) of Eaton. 



Two DIVISIONS — Lower, calcareous, fossiliferous and somewhat fissile ; the upper, shaly, breaking into 



small irregular fragment& 



Color black, usually dark brown when altered. It is the first mass which rises upon the top of the Hcldcrberg series of 

 limestone, and is coextensive with it. It greatly resembles the Utica slate in mineral character, and could readily 

 be confounded with it. 



No. 1. Expanded goniatite (G. eipansus), natural size ; the segment above represents the back of the chambers, which differ 

 iirom No. 2. 



2. Segment of the Marcellus goniatite (G. marcellensis), reduced about one half in size. 



3. Ifimitarjr orthia (O. limitaris). 



4. Marcellus cypricardites (C. matcellensis). 



« 



These shales extend east and west through the district, commencing near the Hudson, and 

 ending on Lake Erie. They are conveniently divided into two masses, from the presence 

 of limestone and fossils in the one, and their absence generally in the other. The limestone 

 is very impure, of the same dark color of the shale, rarely forming continuous layers or beds, 



