GEOLOGY AND PALEONTOLOGY OP THE SCHOHARIE VALLEY 225 



Ithaca beds in the Schoharie region, this replacement however 

 not extending beyond central New York. 



In Blenheim township about 500 feet of this formation has 

 been noted by Prosser, but northeast from this in Moheganter 

 hill, the Ithaca is scarcely represented, the Oneonta beds follow- 

 ing almost immediately on the Sherburne. This shows that the 

 source of the nonmarine sediments was to the northeast. 



The Oneonta beds 



From the Chenango valley eastward the Ithaca is capped by 

 the Oneonta formation which is composed of red and green shales, 

 reddish sandstones and coarse grained grajdsh to greenish gray 

 sandstones. These rocks are nearly unfossiliferous, containing 



Fig. 18 i Archauodon catskillensis 



only an occasional specimen of Archaeopteris and A r c h a n - 

 odon catskillensis (Van.) [fig. 184] . The formation has 

 a thickness of 550 feet in the Ohenango valley, and as the physical 

 conditions under which the Oneonta was deposited appeared 

 earlier to the eastward it gradually thickens in that direction, till 

 in Albany and Greene counties it completely replaces the Ithaca 

 formation.^ 



The fern Archaeopteris jacksoni [fig. 185] may be 

 recognized by its bipinnate frond and obovate pinnules, which 

 narrow toward and are decurrent at the base. The mussel 

 Archanodon catskillensis [fig. 184] is elongated and 

 not unlike Anodonta of the present time. Clarke has shown its 

 significance as an indicator of fresh or brackish conditions.^ 



^Prosser. loc. cit. p. 313-14. 



2 Clarke, J. M. N. Y. State Mus. Bui. 49, p. 199-203. 



