28 NEW YORK STATE MUSEUM 



West River shale 



Succeeding the Genundewa limestone horizon there is a heavy- 

 bed of dark and black shales referred to in the early reports as the 

 upper beds of the Genesee shale. In Ontario county and westward 

 there is a distinctive difference between the lower dark gray fos- 

 siliferous and slightly calcareous shales and the densely black and 

 bituminous shales of the upper part from which they are separated 

 by a few feet of hard blue shales and thin flags. They become more 

 homogeneous toward the east and although the difference is dis- 

 cernible to the careful observer, on the west side of Seneca lake it is 

 not very clearly defined and in the Cayuga lake valley is not recog- 

 nizable. 



For this reason the dark shales that in this quadrangle lie between 

 the Genundewa limestone horizon and the base of the Cashaqua are 

 included in one division as West River shale so named from their 

 abundant exposure in the West River valley in Yates county. The 

 formation is well displayed in the ravine of Plum creek; along the 

 lake shore at Starkey point and the cliffs at the south, near Fau- 

 cetts point on the east side of the lake and in nearly all of the 

 ravines toward the north to Willard. 



• Fossils are exceedingly rare in the upper and more bituminous 

 beds and not at all common in the lower, from which the following 

 species have been obtained : 



Bactrites aciculum Hall Lunulicardium curtum Hall 



Gephyroceras sp. Lingula spatulata Vanuxem 



Pleurotomaria rugulata Hall ■ Orbiculoidea lodensis (Vanuxem) 



Buchiola retrostriata (v. Buck) Liorhyiichus quadricostatum (Fan- 

 Pterochaenia fragilis (Hall) uxem) 



Panenka sp. Melocrinus clarkei JVilliams 



Cashaqua shale 



This formation, which receives its name from its exposure along 

 Cashaqua creek in Livingston county, is there a bed something 

 more than lOO feet thick of light, soft, rather calcareous shale, suc- 

 ceeding black shales and distinctly limited at the top by shales of a 

 like bituminous character. In the Naples valley it is also distinctly 

 differentiated from the shale below and above it, but is decidedly 

 more arenaceous, containing at two horizons bands of sandstones 

 and frequent flags. There is also interstratified in the upper part 

 a thin stratum of limestone of a peculiar character and known as 

 the Parrish limestone that may be easily traced with the blagk 



