GEOLOGY OF THE ATTICA AND DEPEW QUADRANGLES IT 



has been regarded as seriously lessening the value of the limestone. 

 Now, however, this rock is recognized as of great economic im- 

 portance as constituting the best material, when crushed, for concrete 

 work and road-building to be found in western New" York and it is 

 being extensively utilized for such purposes. At some outcrops 

 one or more of the layers may be somewhat shaly, but all the re- 

 mainder is compact and durable and is the source from which have 

 been derived enormous quantities of dimension and building stone 

 of the best quality as well as the purest quicklime. 



At the base of the formation there occurs here 6 to 8 feet of 

 limestone entirely free from chert. This condition is found at 

 nearly all exposures of this horizon, the thickness in a few instances 

 increasing to 25 or more feet. The rock is usually crowded with 

 corals and crinoid stems, and is specially valued for ornamental 

 building stone ; it is also valuable as a flux in the manufacture of 

 steel and is extensively quarried for such use. In the succeeding 

 40 or 50 feet the percentage of silicon is very high, reaching 50 per 

 cent in some localities, while in some of the upper beds it is not 

 more than 10 to 12 per cent. 



This formation is rich in fossils. A list of the various species 

 that occur in it may be seen in New York State Museum Bulletin 

 63, in which there are 3 of fishes, 39 of crustaceans, mostly tri- 

 lobites, 13 of cephalopods, 3 pteropods, 38 gastropods, 15 lamel- 

 libranchs and 48 brachiopods. It also contains many species of 

 corals and crinoids. 



A few of the more common and distinguishing fomis are : 



Odontocephalus selenurus Eaton 



Phacops cristata var. pipa Hall and Clarke 



Gyroceras undulatum {Vaniixcm) 



Gyroceras trivolve [Conrad) 



and the brachiopods 



Atrypa reticularis Linnc 

 Leptaena rhomboidalis VVilckeits 

 Stropheodonta concava Hall 

 S. inequistriata {Conrad) 

 Spirifer acuminatus {Conrad) 

 Sp. divaricatus Hall 



Exposures. The Onondaga limestone is covered by drift in most 

 of the area in the northern part of the Attica quadrangle, where 

 it is the surface rock. The largest outcrop is in the vicinity of an 

 old quarry 2 miles north of Crittenden near the road to Murray 

 where 12 to 15 feet of the upper layers are well displayed. 



