88 Repoet of the State Geologist. 



The Corniferous limestone is of a darker color, less abundant in 

 fossils, and contains much hornstone in courses, from which 

 it derives its name. It is sufficiently distinct in appearance to be 

 separated from the « Onondaga, though the latter also often 

 contains hornstone. 



Seneca limestone is a term given to those courses which overlie 

 the Corniferous layers in Onondaga and Cayuga counties 

 (Yanuxem) and Seneca county (Hall). It is nearly free from 

 hornstone, though certain layers contain it, and the upper tier 

 abounds in it. The presence of certain brachiopods {Chonetes 

 lineata) in large numbers is the mark originally proposed as 

 diagnostic. The term is now scarcely used. 



Since all these parts of the Upper Ilelderberg formation occa- 

 sionally contain hornstone, the word " Corniferous " may properly 

 be applied to the whole. But as hornstone occurs in other 

 geological periods, the preference is given to a geographical 

 name. 



The Onondaga limestone is described in the Eeport for the 

 Fourth District as of a light gray color, often approaching white, 

 more or less crystalline in structure and containing numerous 

 fossils ; in many instances ii seems almost entirely composed of 

 broken and comminuted fragments of crinoidea and corals. 



The only exposure in the county is a piece, now reduced to the 

 length of five feet, forming the top layer at McQuane's quarry, 

 two miles S. W. by W. of the centre of Seneca Falls village. It 

 is two feet thick, covered with a few inches of dirt. . It corre- 

 sponds in every respect with exposures at Phelps ; is very tough 

 (more so than the Seneca limestone) ; its surface is weathered to 

 a deep rusty brown, and is roughened by the projection of great 

 numbers of fragments of crinoids, etc. It contains many entire 

 cyathophylloids, and is destitute of flint nodules. 



The exposure is apparently an isolated one, scarcely rising above 

 the level of the clay plain, at an approximate elevation of 465 feet 

 A. T. The quarry has been worked in the subjacent rock a length 

 of 160 feet, and a depth of 20 feet, giving favorable exposures. 

 Beginning at the lowest exposed layer there are (A) two feet of 

 a strong limestone, described as of a good quality for building, 

 in one course, which has a tendency to split horizontally ; next 

 (B), six and one-half feet, containing considerable impurity, not 



