Handbook of Paleontology 385 



var. armatus, Phacops cristata, Proetus crassimarginatus 

 Calymene platys, etc. 



The Onondaga limestone (Hall '39) has a very wide 

 distribution and extends with very uniform character of 

 the rock and fauna from New Jersey in the southeast, 

 across the State into Ontario, Canada. The name was 

 derived from its occurrence in Onondaga county. The 

 present name now includes all divisions of the formation 

 to which the names Onondaga (Hall), Corniferous 

 (Eaton) and Seneca (Vanuxem) limestone were applied 

 in western New York. The "Corniferous" was the 

 cherty division and the purer upper limestone was the 

 "Seneca." The Onondaga is a moderately pure limestone 

 of light bluish color, often thinly bedded in the lower 

 portion but in general massive. Lenses of chert in 

 parallel layers occur, particularly in the lower part of 

 the formation, but its distribution is very irregular and 

 it has been found to be abundant in some places, sparse 

 in others. The uppermost beds ("Seneca") are free from 

 chert, and often the very lowest beds. The maximum 

 thickness of the Onondaga in the western part of the 

 State is between 150 and 200 feet. The thickness is 

 about 100 feet in the Schoharie area, 85 to 100 feet in 

 the northern Helderberg area and southward from this 

 it thins somewhat until in southeastern New York 

 (Kingston area) it has a thickness of 50 feet or more. 

 At Becraft mountain (Hudson) there is only a thickness 

 of 25 feet, but the Schoharie sandy phase is about 200 

 feet thick here. In the Catskill area the thickness is 

 not a great deal less than in the Helderbergs. The Onon- 

 daga limestone fauna is characterized by corals, an 

 abundance of individuals rather than species. Much of 

 the limestone was probably formed by coral reefs. Among 



