348 A. W. GRAB A U SILURO-DKVOXIC CONTACT IN NEW YORK 



Page 



Trorliociyiis <ji bhardii 1 1 all 371 



Leperditia scaluris .Jones 371 



References 373 



ESxplanal ion of plates 374 



Introduction 



Throughout the greater part of western New York the contact of 

 Siluric with Devonic strata is traceable in the northward facing escarp- 

 ment of the Onondaga limestone terrace. This terrace is a good ex- 

 ample of a cuesta developed on an ancient coastal plain, the drainage 

 adjustment of which has been greatly modified by glacial deposits. The 

 northward facing scarp or " in face " of this cuesta is a prominent topo- 

 graphical feature of western New York, paralleling that of the Niagara 

 cuesta which lies from 15 to 20 miles farther to the north. 



The inface of the Onondaga cuesta first appears in Erie county, in the 

 northern part of the city of Buffalo and a mile or two east of the Niagara 

 river. Between this point and the river, extensive drift deposits have ob- 

 scured the cliff,which, however, has been definitely located by excavations 

 and borings.* From the point of its first appearance on Scajaquada creek 

 eastward, it increases in prominence and elevation, until at the county 

 line it is about 80 feet in height, increasing to about a hundred feet in 

 Genesee county. Between Buffalo and Williamsville the cliff is divided 

 into two parts, with a flat terrace of varying width up to 200 yards sep- 

 arating them. This division is along the line of contact between the 

 Siluric and the Devonic. At Williamsville, Ellicott creek descends in 

 a series of falls over the cliff, producing very good natural exposures of 

 the strata. At Harris hill and Clarence hollow other small streams 

 descend northward over the cliff. At Falkirk, Murder creek has cut a 

 gorge of some magnitude into the northern face of the cuesta, over which 

 it descends, likewise in a series of small falls and rapids. All these 

 streams are tributary to the Tonawanda, which has another branch, 

 bearing its own name, descending over the cliff at Indian falls, several 

 miles east of the county line. 



The summit of the cuesta is formed by the resistant Corniferous beds 

 of the Onondaga limestone series, while the more fossiliferous, chert-free 

 lower beds of this series and the Manlius limestone and the Waterlime 

 lie at the base. The latter rock is rarely exposed in its totality in Erie 

 county. 



* Bishop, 1895, |>. 312. 



