164 NEW YORK STATE MUSEUM 



below Portage. It is generally recognized by its black, soft, slaty 

 texture, but its fossils are very rare. 



Portage group 



This name has been given to the next higher portion of the 

 great slaty and shaly masses, which form the walls of deep gorge 

 of the Genesee at Portage and cover everywhere on the south 

 the Hamilton group and Genesee slates. This enormous pile of 

 sandy, slaty and shaly strata is in some parts of the state 1,000 

 feet in thickness : it was divided by Prof. Hall into a lower mass 

 called the Cashaqua shale, a middle mass called the Gardeau 

 shale and flagstones, and a terminal mass of sandstones seen at 

 Portage; but in middle and eastern New York, these divisions 

 are not distinct. 



Much of this group is a soft olive-colored shale; but its most 

 useful portions are its layers of flagstone, which are largely quar- 

 ried near Norwich and Ithaca, on the hills back of the Helder- 

 bergs, on those west of the Hudson river as far down as Rondout; 

 and in Sullivan county near the Delaware river. 



From Chenango and Broome counties eastward to Greene 

 county the Portage is represented by the Oneonta formation 

 which forms the lower 1,000 feet of the Catskill mountain strata. 



The soft shales of the Portage group contain many of the con- 

 cretions known as Septaria, which also occur in the Marcellus 

 shales. 



Chemung group 



To the Portage succeeds the Chemung, so called from being 

 well exhibited at the ' Narrows ' of the Chemung river, near 

 Waverly, in Tioga county. Its thickness of 1,000 or 1,500 feet is 

 made up of a series of thin-bedded sandstones with intervening 

 shales and occasional beds of impure limestone mainly formed 

 by the materials of fossil shells. In many places it abounds 

 with fossils. While well developed in central and western New 

 York the Chemung, as a group of fine sediments, disappears to 

 the eastward and is represented by the Catskill formation. 



