CORNIFEROUS LIMESTONE. 



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20. CORNIFEROUS LIMESTONE. 



No. 1. Head and tail of the Moon-tail odontocephalns (0. 

 selenuras). 



2. Undulated cyrtoceras (C. undulatus), reduced one- 



thiid in size. 



3. Undulated strophomena (S. undulatus). 



No. 4. Lenticular orthis (0. lenticularis). 



5. Priscan atrypa (A. prisca). 



6. Linear strophomena (S. lineata), magnified twice llie 



natural size. 



7. Fish-bone (Ichthyodorulite). 



Under this head, the Seneca limestone of the Reports is also included ; the two masses, 

 however, are separately considered, and in the order of their succession, merely from the 

 presence and great abundance of a single fossil species in the upper one. These limestones 

 are the terminal members upwards of the Helderberg division of the New- York system. 

 Above and resting upon this division, the thick masses of shale and sandstone comrrience, 

 which extend south into Pennsylvania, and pass under the coal of that State, being the sup- 

 port of that deposit, and the termination upwards of the New-York system of rocks. Above 

 the Helderberg division, there are no more masses of limestone in the district, or the State, 

 that extend through the district, but partial masses only, the most extensive of which is the 

 Tully limestone, which makes its appearance only at the west end of Chenango county, and 

 continues through Onondaga and Cayuga counties into the fourth district. 



Comiferous limestone is one of the names given by the late Prof. Eaton, in the survey of 

 the Erie canal. It is retained, as being apphcable to this rock ; for it contains flint or horn- 

 stone in nodules, in one or two layers, throughout the whole extent of its range. The 

 nodules are arranged in parallel layers, firom two to ten in number. It is a character not to 



