CORNIFEROUS LIMESTONE. 
20. CORNIFEROUS LIMESTONE. 
No. 1. Head and tail of the Moon-tail odontocephalus (O. No. 4. Lenticular orthis (0. lenticularis). 
selenurus). 5. Priscan atrypa (A. prisca). 
2. Undulated cyrtoceras (C. undulatus), reduced one- 6. Linear strophomena (S. lineata), magnified twice the 
third in size. natural size. 
3. Undulated strophomena (S. undulatus). 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 commence, 
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. 
Corniferous limestone is one of the names given by the late Prof. Eaton, in the survey of 
the Erie canal. It is retained, as being applicable 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, from two to ten in number. It is a character not to 
