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NEW YORK STATE MUSEUM 



Regarding the identity of the Cobleskill of the cement region 

 as established it becomes apparent that the Brayman shales are 

 the approximate stratigraphic equivalents of the Rosendale cement 

 bed. As before noted however, the indication of an hiatus at the 

 top of the Brayman shales makes absolute equivalency doubtfuL 

 The Rosendale cement bed of eastern New York appep^rs also to be 

 the stratigraphic equivalent of the Bertie formation, or at least a 

 part of it in western New York. That formation averages 60 feet 



y 



\ 





"'(^n. 



Fig. 30 Favosites niagarensis 



in thickness at Buffalo, though only the upper 8 or 10 feet carry 

 the Eurypterus fauna. It is therefore probable that the Rosen- 

 dale bed oorresponds only to the upper part of the Bertie, while 

 the underlying sandstones and conglomerates (Shawangunk beds) 

 probably are the equivalent of the lower part of the Bertie, as well 

 as part of the remaining fSalina beds.^ 



^Tbe impropriety of considering the Shawangunk grit basal Siluric in 

 age will be apparent when we consider that it rests ii neon for mahli/ on 

 the folded Hndson river strata in which are included the Lorraine or 

 Upper Champlainic beds. It w^ould be necessary to assume that the folding 

 and extensive erosion which the Hudson river beds suffered after Lorraine 

 time was all accomplished during the interval represented by the Richmond 

 beds of the west. Thus very little time is allowed for the folding and 

 erosion of the Champlainic beds, if the succeeding beds are considered 

 basal Siluric, i. e., Premedina as is the general practice. If however we 

 consider the Shawangunk grit of Salina age, the folding and erosion of the 

 Champlainic beds could have been accomplished during Palaeo- and Meso- 

 Siluric time. 



