42 



NEW YORK STATE MUSEUM 



These shales are contrasted with the Genesee shales below by 

 their lighter color and less bituminous character, being mostly 

 highly fissile and breaking into thin sharp laminae. 



The concretions are highly characteristic of these beds and in 

 the region of their outcrop have been collected extensively on 

 account of their curious shapes suggestive of turtle backs, human 

 skulls and other rounded objects. Fossils are common but nowhere 

 abundant. Fine specimens are occasionally found in the concre- 

 tions. 



The following species occur in the beds: 



Bactrites aciculum Hall Pterochaenia fragilis Hall 



Gephyroceras sp. Lunulicardium curtum Hall 



Pleurotomaria rugulata Hall Lingula spatulata Vanuxem 



Buchiola retrostriata v. Buck. Orbiculoidea lodensis Vanuxem 



Panenka sp. 



The West River shale is exposed on the Penn Yan quadrangle 

 at the mouth of the Sartwell ravine i mile south of Penn Yan; 

 also in a small ravine on the north side of the Keuka outlet i mile 

 east of Penn Yan and on the east side of the Potter swamp along 

 the road leading eastward to Voak. 



Other good exposures may be found in the ravine of Plum creek 

 below Himrods ; along the shore of Seneca lake at Smith's point in 

 the town of Starkey, and at Faucetts point i mile farther north 

 on the east side ; in the Goodrich and other ravines in West River 

 valley in the town of Middlesex ; in several larger ravines on the 

 sides of Canandaigua lake from Seneca point southward ; in ravines 

 along the sides of Conesus lake ; in the cliffs at the mouth of the 

 Genesee River gorge at Mt Morris ; in the ravine at Griswold 6 miles 

 west of Attica and on the shores of Lake Erie near the mouth of Pike 

 creek in the town of Evans, Erie co. 



On the western border of this quadrangle the West River shale 

 has a thickness of no feet and is overlain by a lighter colored and 

 somewhat arenaceous band known as the Standish shales and 

 flags, which are succeeded by a heavy bed of black shales called 

 the Middlesex shales. 



By a gradual change in the character of the sedimentation the 

 identity of these formations is lost before reaching the exposures 

 of their horizons in the northeastern part of this quadrangle, the 

 Standish flags being eliminated from the rock section and the 

 Middlesex black shale appearing, if at all, only as a few feet of 

 darker and more bituminous shale at the top of the West River 

 shales not separate from the latter formation, and the upper 

 limit of the West River shale is not well defined. 



