26 NEW YORK STATE MUSEUM 



For these and other reasons more fully set forth in Museum 

 bulletin 63, the use of the term Genesee shale is restricted to beds 

 between the Tully and the Genundewa limestones in Ontario county 

 and westward and, on these quadrangles where the latter does not 

 appear, to a band of calcareous shales and row of fossiliferous con- 

 cretions in its horizon. 



The Genesee shale is a homogeneous mass of densely black thinly 

 laminated bituminous shale that after exposure becomes fissile and 

 splits into flat plates. The beds are usually traversed by approxi- 

 mately parallel series of joints that intersect each other at different 

 angles producing on the surface of horizontal exposures triangles, 

 diamonds, rhomboids and other kindred forms, and in cliffs striking 

 effects like bastions and buttresses. In old exposures the outward 

 angles have been worn away and there are left rounded masses of 

 black shale partly covered in sheltered places by a thin white 

 efflorescence of alum produced by the decomposition of the con- 

 tained iron pyrites. The formation is 90 feet thick on the Keuka 

 outlet and 75 feet at the east line of the quadrangle. 



It is usually exposed more or less favorably wherever the Tully 

 limestone crops out but the following are some of the more accessi- 

 ble localities where it may be seen : in the cliffs and ravine on the 

 south side of the Keuka outlet at Cascade mills ; in the lower 

 part of the ravine of Plum creek; along the lake shore and in 

 ravines between Miller point and Starkey point; on the east shore 

 between Faucetts point and Lamoreaux Landing; in all of the 

 ravines in the vicinity of Lodi Landing; in the railroad cut at 

 Willard ; in the highway north of Ovid, and in all of the ravines 

 southeast of Hayt Corners. 



Fossils are exceedingly rare in the Genesee shale, the densely 

 black portion being practically barren though an occasional lignite 

 and a few conodont teeth are found in them. ' 



The less bituminous shales contain: 



Pleurotomaria rugulata Hall Liorhynchus quadricostatum 

 Styliolina fissurella Hall (Vanuxem) 



Pterochaenia fragilis (Hall) Probeloceras lutheri Clarke 



Lingula spatulata Vanuxem Bactritts aciculum (Hall) 

 Orbiculoidea lodensis (Vanuxem) 



Genundewa limestone horizon 



In Ontario county and westward to Lake Erie the Genesee shale is 

 succeeded by a band of thin nodular limestones composed princi- 

 pally of myriads of the minute shells of Styliolina fissu- 



