BIGSBY PALAEOZOIC ROCKS OF NEW YORK. 375 



With Schoharie Grit, says James Hall (Pal. i. xvii.), commences 

 a series of fossils as distinct from those of the preceding formations 

 as these from the lower division. We must, indeed, unite all the 

 succeeding strata as Devonian ; but the three divisions are only three 

 terms in one system. 



This rock contains many fossils, but they have not been regis- 

 tered. 



We know of the presence in it of three Brachiopoda — Atrypa im- 

 pressa, Hall, Chonetes hemisphtzrica, Hall, and Pentamerus aratus, 

 Hall, — with Phacops macrophthalmus and certain Orthocerata having 

 cross-rings. There is a Cyrtoceras like that of the Eifel on the Rhine. 

 There is also a Pleurorhynchus of the size of some Carboniferous 

 species ; and numerous Corals occur (De Verneuil, loc. cit.). 



Onondaga Limestone. 



Mineral Character. — It is usually a pure limestone (Vanuxem), 

 of a light-grey colour, and crystalline. Sometimes it is darker and 

 more compact in texture, with its layers separated by green shale in 

 seams. 



In some localities it contains numerous nodules of flint in parallel 

 layers (Vanuxem, p. 135). It looks like the Wenlock Limestone of 

 England, but the latter has more intermixed shale. The lower layers 

 of the limestone at Splitrock Quarry frequently hold black pebbles, 

 distinctly waterworn, and identical with the sandstone-nodules, or 

 accretions, of Oriskany Sandstone, south of Paris Hill, near Eastman's 

 Quarry (Vanuxem, p. 137). 



Place. — The impure limestone ending the Onondaga-Salt group 

 is succeeded by the Onondaga Limestone, with a few inches of sand- 

 stone between them. This takes place throughout all Western New 

 York, where the Waterlime group, Lower Pentamerus limestone, 

 Delthyris shaly limestone, Upper Pentamerus limestone, and the 

 Oriskany Sandstone and its two subordinate grits are wanting. 



Onondaga Limestone also rests at Paris Hill and on the west side 

 of Oneida Creek on Oriskany Sandstone. In another place it lies 

 upon the Waterlime group. 



This limestone extends from the Helderberg Mountains to near 

 Lake Erie in unbroken continuity (Vanuxem, Rep. p. 132), but 

 remarkably thin in comparison with its extent. Professor Troost 

 found it in the State of Tennessee, marked by its typical Echinoderm, 

 the Encrinus Icevis. 



The range of this limestone, according to another observer (Hall, 

 Rep. p. 151), is in an undulating line, having a general east and west 

 direction, which extends eastwards to the Hudson River, and west- 

 wards far beyond the River Niagara into Canada. Its northern outline 

 is everywhere distinct, forming, together with the next succeeding 

 rock, the second great limestone-terrace, which rises to the south of 

 the valley, marking the range of the Onondaga-Salt group. 



Transition. — This is abrupt. A pure limestone : this rock has no 

 connexion with the preceding stratum, which may be one of several. 



