46 NEW YORK STATE MUSEUM 



Classification 



The rock strata of the Genesee river section have been broadly 

 classified and generally known under the names " Genesee," for 

 the black shale at the mouth of the gorge, " Portage " for the shales 

 and sandstones displayed above in the walls of the gorge, and 

 " Chemung " for the sandstones and shales exposed in the ravines 

 and along the river bed south of Portage to the State line, names 

 applied at the time of the first geological survey of the State, 1837 

 to 1843. 



In this bulletin the precise and detailed classification of these 

 rocks defines more exactly the significance of each of these appella- 

 tions, as explained under the appropriate titles. Of most com- 

 manding importance in the rock succession of this region is the 

 series of strata historically known as the " Portage Group." To 

 validate the integrity of this term against incursion its origin and 

 purpose are here briefly recalled. 



The name " Portage " was first used in connection with the geo- 

 logical series of the State by James Hall in 1840 (Fourth Annual 

 Report on the Fourth Geological District), when describing with 

 some detail the rock section exposed in the Genesee River gorge 

 between Mount Morris and Portageville. The following divisions 

 were made : Cashaqua shale, Gardeau or Lower Fucoidal group 

 and Portage or Upper Fucoidal group. 



The last division included the strata between the Table rock at 

 the top of the Lower Portage falls and the top of the heavy sand- 

 stones above the Upper falls, an aggregate of 425 feet of which 

 210 feet are shales and flags, not essentially different either in 

 lithology or fossils from the beds below the Table rock and included 

 in the Gardeau group, except as to the presence in the upper of 

 Fucoides verticalis. 



In 1843 (Final Report on the Geology of the Fourth District, 

 page 224), Professor Hall dropped the terms "Upper Fucoidal" 

 and " Lower Fucoidal," and the expression " Portage or Nunda 

 group " is employed to include " Cashaqua shale," " Gardeau shale 

 and flags " and " Portage sandstones," no change being made in 

 the descriptions of these members of the Portage group. 



It thus appears that the word " Portage " was first used as a 

 group term, not as the description of a member of a group or unit. 

 It was so employed by Hall in all subsequent writings. 



