^4 NEW YORK STATE MUSEUM 



rence of its characteristic marine fossils, then several hundred feet 

 more of rocks may be noticed as intervening between the upper 

 Portage rock and that group. The rock succeeding the upper 

 Portage rock consists of greenish olive, sandy shale, or very shaly 

 sandstone, never slaty. The only fossils seen in this rock is a 

 species of fucoides with a striated surface, and these are by no 

 means numerous. This is succeeded by a dark, nearly black sandy, 

 highly micaceous shale with septaria. It contains iron pyrites and 

 where exposed is of an iron rust color externally. Some thin 

 masses of gray sandstone are interstratified which contain fossils 

 referable to the Chemung group. 



[p. 402] Succeeding the black micaceous shale are the sandstones 

 and shales constituting the Chemung group which is everywhere 

 visible in the ravines and banks of streams. Its northern limit 

 extends through the southern part of the towns of Centerville, 

 Hume, Grove and Burns. In this county more particularly along 

 the Genesee river and west, the group differs in Hthological char- 

 acters and consequently in some degree from the same rocks in 

 Steuben and Chemung. 



From these quotations it is clear that though Hall conventionally 

 classified all of the rocks succeeding the Portage (Nunda) sand- 

 stones for a thickness at least as great as appears on these quad- 

 rangles, as belonging to the Chemung group, he directed attention 

 to the fact that they might be subdivided as follows : 



1 Olive shales and shaly sandstones at the base. 



2 Micaceous shales with thin sandstones containing brachiopods. 



3 Heavy sandstones and shales which, lithologically are very 

 similar in character to the strata referred to as constituting the 

 Chemung group at the type locality. 



Sufficient data have not yet been obtained on which to decide 

 whether divisions 2 and 3 should be considered as separate geologi- 

 cal units, but it is not improbable that further invesigations may 

 demonstrate that they are such. 



The beds of division i are known as the 



Wiscoy shales and sands 



These shaly olive beds were described as a unit in the New York 

 geological series, and the relations of the fossils found in them 

 discussed by Clarke in the i6th Annual Report of the State Geolo- 

 gist of New York, 1898, and the name " Wiscoy shales and sands " 

 applied to them on account of their favorable exposure at the falls 

 of Wiscoy creek at Wiscoy, N. Y. 



The stratigraphy of these beds was shown in detail in diagrams 

 accompanied by description, by Luther in New York State Museum 

 bulletin 69, 1903. 



