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NEW YORK STATE MUSEUM 



deposition. The confirmation of this conclusion as to the value 

 of the Shawangunk grit was afforded by the discovery of an 

 extensive eurypterid fauna in the interbedded shales of the Shawan- 

 gunk grit, as described by the writer [see op. cit. p. 294]. Mr 

 Hartnagel has indicated the improbability of this Siluric age of 

 the Rensselaer grit or its equivalence to the Oneida-Medina sedi- 

 ments with the following arguments: (1) the extensive gap by 

 nondeposition between the eastern terminus of the Oneida con- 

 glomerate, in Herkimer county, and the Rensselaer grit plateau,. 

 (2) the long time interval which must be postulated to account 

 for the Taconic folding and the erosion that preceded the deposi- 

 tion of the grit, (3) the gradual transgression northward of 

 arenaceous sediments over the eroded folds, the Shawangunk grits 

 being a more southerly and hence earlier representative of such 

 transgression. 



The region of the Rensselaer grit has recently been carefully 

 searched for fossils but though this evidence still fails and its 

 absence can not be explained by secondary changes in the rocks, 

 the stratigraphic considerations indicate the propriety of assigning 

 a distinctly later than [Medina age to this formation. 



Near the edge of this plateau no beds of later than Trenton age 

 have been observed and there are apparently no outliers to bridge 

 the gap between the late Siluric and early Devonic outliers of 

 Becraft mountain, Mt Bob and the southernmost outliers of Rens- 

 selaer grit in the town of Austerlitz, Cokimbia co. This last 

 named outlier is of especial interest as it lies but 20 miles north- 

 east of Becraft mountain and is a considerable distance south of 

 the main Rensselaer grit plateau. For these reasons it has been 

 closely studied but found to be in no way lithologically different 

 from the grit of Rensselaer county at the north, containing the 

 same alternations of grit with red and greenish slates. 



From the presence of only the closing stage of the Upper Siluric 

 at Becraft mountain and in the Helderberg near Albany (Country- 

 man hill), — the two places where the deposits of the Siluro- 

 Devonic basin of New York approach nearest to the Rensselaer 

 grit plateau — it may be properly inferred that the Upper Siluric 

 sea of New York did not extend into the present area of the 

 Rensselaer grit plateau at any time except possibly in the latest 

 (Manlius) stage of that period. In regard to the latter, the prob- 

 lem is the same as in regard to the Helderberg limestones in 

 general which are exposed at Becraft mountain and of which the 

 Rensselaer grit might be conceived as representing the littoral 



