BIGSBY — PALiEOZOIC ROCKS OF NEW YORK. 373 



to denudations or to natural inequalities in the surfaces of pre-exist- 

 ing rocks." (De Vern. loc. cit.) 



Its position (Vanuxem, Rep. p. 123) is best seen in the south-east 

 side of New York, near Salem, — the geographical division " Helder- 

 berg" being there complete. It projects from the side of the Hel- 

 derberg Mountain, and forms a terrace resting upon Delthyris shaly 

 limestone, the Oriskany Sandstone passing under, and covered up 

 by, the Caudagalli Grit. Mather has only seen it in the south-east, 

 on Schoharie Mountain and at Clarkville (p. 340). 



It occupies part of the counties of Madison, Onondaga, Genesee, 

 &c. In the eastern and central parts of the State its immediate 

 associates cease entirely (Vanuxem) before reaching the west end of 

 Madison County ; and the Oriskany Sandstone rests at Manlius 

 upon the Waterlime group, and is covered by the Onondaga Lime- 

 stone, as at Perryville, — these three rocks extending, thus connected, 

 to Lake Cayuga. 



The localities at which this rock is visible are more numerous on 

 the west side of Central New York than on the east side. 



As Daniel Sharpe expresses it, this sandstone, the Caudagalli Grit, 

 and Schoharie Grit are "beds of the same age, locally distributed." 



Transition. — Its mode of passage from the subjacent rock is only 

 mentioned twice — at Helderberg and at Oriskany Village. It there 

 rests upon Delthyris shaly limestone, into which it graduates, con- 

 taining multitudes of the Atrypa Icevis of the latter rock. 



Position. — It is conformable to the strata about it. 



Thickness. — This rock in New York varies in thickness from two 

 to seventy feet. It is usually thin in this State, and often in patches. 

 In Pennsylvania, according to Rogers, it is a more constant stratum, 

 and averages 700 feet in thickness. 



Fossils. — This is a rock of great geological importance ; for on 

 entering it we lose the older fossils, except three Atrypce (Icevis, ema- 

 cerata (?), and reticularis), Spirifer niagarensis, and S. plicatus. 



As far as is now known, twenty-nine new species are introduced, of 

 which 26 are Brachiopoda — 6 Rhynchonellce, 4 Leptcence, 5 Spiriferi, 

 3 Orthides, 3 Atrypce, 2 Chonetes, 2 Meganteres, and 1 Leptocelia. 

 It receives and transmits 5 Brachiopoda and 1 Zoophyte into the Cor- 

 niferous Limestone (Hamilton Group or Chemung), besides the 

 universal Cornulites serpularius. 



The fossils are mostly at the base of the rock, crowded and very 

 large, — the most common being Spirifer arenarius, Atrypa elongata, 

 and A. unguiformis of Conrad (Vanuxem, Rep. p. 123). They are 

 all casts, except where the rock is slightly calcareous. The genus 

 Spirifer, which has hitherto in the different groups been only of 

 small size, here becomes large, and presents species which, by their 

 dimensions and their numerous plications, approach the Devonian 

 and Carboniferous types. 



The plant we find here is a branchless, pipe-like fucoid. It is 

 straight, and stands vertically in the stratum. 



In 1854 James Hall wrote that he expected to describe nearly sixty 

 species from this sandstone. 



