26 NEW YORK STATE MUSEUM 



gastropods, 8 cephalopods and 2 frilobites, besides crinoid stems and 

 unidentified corals. 



For list of species see Sixth Annual Report of the State Geologist, 

 1887. 



Genesee black shale 



This term was formerly used to designate all of the thick mass of 

 black and dark shale that succeeds the Tully limestone, up to the base 

 of the light colored Cashaqua shale, but for reasons fully set forth 

 in State Museum Bulletin 118, it is now applied only to the more 

 densely black and bituminous lower beds that lie between the Tully 

 limestone and a thin but well defined, calcareous band known as the 

 Genundewa limestone that from Ontario county westward to Lake 

 Erie separates the beds formerly called the lower Genesee shales 

 from the somewhat lighter colored and more calcareous upper 

 Genesee shales. 



The limestone is absent in the Cayuga lake valley but the upper 

 limit of the Genesee shale is well marked by an abrupt change to a 

 light gray calcareous shale in the place of the limestone. Two hard 

 layers i foot 6 inches and 12 inches thick near the base of the Genesee 

 in the southern part of the Genoa quadrangle are impure limestone but 

 as the few fossils they contain are of the species found in the higher 

 beds, they are, as previously stated, classified as Genesee. There are 

 also a few calcareous concretions but otherwise this formation is 

 quite uniform in character from bottom to top. Though fissile after 

 exposure the rock when fresh is compact and quite hard, and is less 

 susceptible to erosion than more clayey shales. The beds are usually 

 traversed in two or more directions by vertical joints that divide the 

 surface in small square, triangular or diamond shaped tesselations r 

 to 3 or 4 feet across. 



Fossils are not abundant in the Genesee shale but the collector may 

 expect to find : 



Liorhynchus quadricostatum Hall Pleurotomaria rugulata Hall 



Chonetes lepidus Hall Styliolina fissurella {Hall) 



Lineula spatulata Hall Tentaculites gracilistriatus Hall 



Orbicnloidea lodensis (Vanuxem) Probeloceras lutheri Clarke 



Pterochaenia fragilis (Hall) Bactrites aciculum {Hall) 



The Genesee shales are exposed in the cliffs on the east si^^e of the 

 lake near the south line of the quadrangle and at most of the ex- 

 posures of Tully limestone previously mentioned. This formation at- 

 tains its greatest thickness in this State, about 100 feet, in Ontario 



