140 The Llf('-Hisionj (if Spirifrr IcPfis. 



X. — The Liff'-IIisforji of Spinfer he vis, Hall: — a Falceonto- 

 lugicaJ Study. 



ItY IIENKV y. WILLIAMS. 

 Kead April 25th. 1881. 



In middle and western New York, cropping out also in some 

 localities westward and southward, appears a series of shales and 

 shaly sandstones known as the Portage group. 



The total thickness of the seiies, as defined by Hall, is from 

 1000 to 1400 feet in the western part of New York State. Leslie 

 defines 1450 feet of Portage Flags in Pennsylvania. 



The ''Erie shales*' of Newberry arc considered as the same 

 rocks in Ohio, where they thin out and disappear west of the 

 Vermilion Eiver. 



Rocks corresponding to the upper layers of the Hamilton 

 Period, or lower part of the Portage, are found further west, 

 and are called "Black slates," or '"Bhutk shales," — the ''Huron" 

 in Ohio, and the "Huron group," Winchell. in Michigan. • 



Although the line between the Hamilton and Chemung 

 Periods is not clearly defined in these western outcrops, these ■ 

 "black shales" and "Huron" slates are ai:»parently more closely 

 connected historically with the Hamilton Period than with the 

 Chemung ; and we may regard the true Portage shaly sandstone, 

 in which the characteristic fossils occur in western New York, 

 as limited in outcrop to middle and western New York, Ohio 

 and Pennsylvania, 



In the upper part of the Portage beds, in a few localities only, 

 has been found a large, smooth-surfaced, unplicated fossil of the 

 genus Spinfer, described first by Hall, in the Geological Eeport 

 of the Fourth District of New York, 1843, p. 345, fig. 1, under 

 the name of DeWiyris Iceris. This was afteiwaids (1867) more 

 fully described and carefully figured in the fourth volnme of 

 the Palgeontology of New York as SjHrifera Icevis (1. c, p. 339, 

 pi. XXXIX) by James Hall. In the latter description, two 



