500 NEW YORK STATE MUSEU^r 



to the Hudson river group, as indicated by Matlier in 1843, and 

 certainly to some member of the Trenton period ".^ 



But it seems to the writer that the evidence afforded by these 

 fossils has been here somewhat^strained to bring the facts into 

 accordance with Hall's views; for, while Orthis testudiiv- 

 aria, Leptaena sericea, Strophomena alter^ 

 nata, Bellerophon bilobatus are noncommittal, oo 

 curring from the Ttenton to the Lorraine beds, and B y t h o^ 

 trephis subnodosa, being a rather indistinct plant frag- 

 ment, is of little or no taxonomic value, Orthis pectinella 

 Ifi declared by Hall himself (7:128) to occur in nearly every 

 part of the Trenton limestone, though unknown to him in the 

 Hudson river group. Theodore G. White, in his very useful 

 paper (51:88, 94), reports the form only from a six fo'ot bed 

 overlying the Black river limestone of the Poland limekiln seo- 

 tion. In the Cincinnati region and in Canada the fossil is found 

 in the Black river and Tl'enton beds, and Winchell and Ulrioh 

 announce it in their carefully prepared lists only from the upper 

 Black river beds of Minnesota (49). 



The evidence afforded by the fossils of Poughkeepsie would 

 then rather indicate for these Hudson river schists the age of the 

 Trenton limestone. 



J. D. Dana and W. B. Dwight 



At the same time the problem of the Hudson river shales was 

 approached from the east by James D. Dana (21), whcr found 

 that the five limestone belts traversing the schists east of the 

 Hudson river are anticlines of limestones, underlying the schists. 

 He also succeeded in finding fossils in the limestones which were 

 described by W. B. D wight (23), as denoting a Trenton fauna- 

 Dana, therefore, concluded that the " Taconic schists '' overlying 

 the limestone are of Hudson river age. 



Dwight cites the following fossils : Orthis tricenaria, 

 O. pectinella, O. testudinaria, Leptaena seri- 



^Dana had meanwhile (Manual of geology. 1874) proposed to unite the 

 Trenton, Utica and Cincinnati (= Liorraine) epochs under the term Trenton 

 period. 



