Clarke — The Naples Fauna. 



33 



The beds which lie directly above what was there termed the " upper 

 black shale " (thus contradistinguished from the " lower black shale," the 

 former now known as the Genesee slate and the latter as the Marcellus shale) 

 were designated as the Cashaqua shales, taking their name from the creek 

 entering the Genesee river from the east at Mt. Morris. These are olive-green 

 or grey clay shales alternating with bituminous shaly beds and with inter- 

 bedded thin shales, sandstones and flags. Upward in the rock series there is 

 in general, a gradual increase in the amount of arenaceous sediment, the sands 

 and flags becoming increasingly predominant and the shale beds themselves 

 more arenaceous. While the transition to these beds from those below is in 

 all respects an easy one, yet there is a possibility of distinguishing them in 

 the mass, and hence the upper beds were termed the " Gardeau or Lower 

 Fucoidal Group"; the adjective term referring to the abundance of the so- 

 called u Fucoides grapliica " over the lower surfaces of the flags. A thick mass 

 of heavy bedded greenish or grey feldspathic and quartz sandstones above 

 the Gardeau flags, representing the culmination of arenaceous sedimentation of 

 this cycle, was termed the "Portage or Upper Fucoidal Group " ; many of the 

 layers containing vertical annelidan borings filled with mud, which have com- 

 monly passed under the name of " Fucoides verticaMsP 



In recognition of the fact that the distinction thus instituted in parts of 

 this series would be difficult of application in actual practice, the same author, 

 in 1843, applied the term "Portage or Nunda Group" to the entire series 

 lying between the uppermost beds of the Genesee slate and the upper limit of 

 the heavy beds of Portage sandstones. Since that date not only have the 

 rock strata thus delimited in these western sections of New York, been 

 known in geologic literature as the " Portage Group," but this term has been 

 also, and properly, applied to all formations in whatever sections of this 

 State and bearing whatever faunas, between the horizon of the Genesee slate 

 beneath and the earliest strata characterized by the incoming Chemung fauna 

 above. 



Recent investigations indicate that the historical delimitation of the 

 Portage group in the typical Genesee section does not express the complete 

 upward range of the fauna of this group. In the Genesee valley, the Portage 

 sandstones are overlaid by sandy shales and thin sandstones from one to two 

 hundred feet in thickness and, in lithologic character, not unlike the Gardeau 

 layers beneath ; and through these beds the Naples or Intumescens-fauna 

 ranges, with slight accretions. Strictly speaking, this fauna is mainly confined 

 to the more argillaceous layers, Avhile toward the top, a Chemung fauna 

 3 



