DEVONIAN. 301 



The Onondaga limestone, as the term has been apphed since 1894, comprises a 

 lower and an upper member called by HalP^"^ "Onondaga" and "Corniferous," 

 respectively, and covers the original application of the descriptive name "Cornif- 

 erous" of Eaton. The extension of the geographic term Onondaga to the whole 

 was made by Hall.^^® In 1843 HalP®^ described the lower member thus: 



Throughout the greater part of the Fourth district the impure Hmestone terminating the 

 Onondaga salt group is succeeded by the Onondaga limestone, with usually the intervention 

 of a few inches of sandstone before noticed, which in ordinary observations might be entirely 

 overlooked. There is also sometimes a thin band of nonfossiliferous bluish-gray limestone. 

 The range of this formation is in an undulating line having a general east and west direction 

 throughout the district, extending eastward to the Hudson River and westward far beyond 

 the Niagara into Canada. Its northern outline is everywhere weU marked, 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. 



This rock is subordinate in thickness and continuation to the next succeeding mass, and 

 was not separated from that by Prof. Eaton. Indeed for aU practical purposes they may 

 be regarded as one formation, the lower part, where fully developed, being marked by an 

 assemblage of fossils which sufficiently distinguish it. 



Its usual characters in the Fourth district are a light-gray color often approaching to white, 

 more or less crystalline in structure, and containing numerous fossils. In many instances this 

 mass, like the encrinal limestone at Lockport, seems almost entirely composed of broken and 

 comminuted fragments of crinoidea and corals, sometimes extremely attenuated, and at other 

 times fragments of large size are preserved. 



Sometimes the mass is fine grained, more compact in texture, and of a darker color; when 

 it has this character, few fossd remains are detected in it. The layers are usually separated by 

 thin seams of greenish shale, which often divide blocks of the stone into wedge-form and 

 irregular laminse. 



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The Onondaga limestone in many places contains nodules or thin interrupted layers of 

 chert or hornstone (usually called flint), and sometimes the Favosites are partially dissolved 

 and the cavities lined with silex in the form of chert, chalcedony, or crystals of quartz. The 

 alimentary canal of the crinoidal columns is frequently lined with crystals of quartz, and the 

 chambers of Orthocera, as weU as the cavities of other shells, often present the same appearances. 



Its characteristic features, when well developed, and which are always much more prominent 

 than the lithological or minera,l characters, are the presence of Cyathophylli, Favosites, and frag- 

 ments of crinoidal columns. These always accompany it in situations where it is sufficiently 

 developed to be of much importance either in economical consideration or geological interest. 



Regarding the upper member of the Onondaga limestone HalP*"'' says: 



This rock is one of the most persistent of any in the series, and at the same time maintains 

 a uniformity in lithological character and in the occurrence of certain fossUs scarcely possessed 

 by any other. It is known to extend from the Helderberg j\Iountains, on the Hudson River, 

 to the Niagara River, and thence far into Canada. 



* * * * * * *'* * 



Under the Corniferous limerock of Prof. Eaton were included this rock and the Onondaga 

 limestone of the reports, the latter constituting his "Ceratial rock," so named from the abun- 

 dance of Cyathophylli which it contains. The name Corniferous is continued as being pecul- 

 iarly applicable to this rock, though the other limestones contain the same mineral. This 

 is the highest limestone of importance in the series, which continues tlu-oughout the district. 



