EARLY DEVONIC HISTORY OF NEW YORK AND EASTERN NORTH AMERICA I 59 



the discovery of an extensive eurypterid fauna in the interbedded shales of 

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

 Hartnagel has indicated the improbability of this Siluric age of the Rens- 

 selaer grit or its equivalence to the Oneida-Medina sediments with the 

 following arguments : (i) the extensive gap by nondeposition between the 

 eastern terminus of the Oneida conglomerate, in Herkimer county, and the 

 Rensselaer grit plateau, (2) the longtime interval which must be postu- 

 lated to account for the Taconic folding and the erosion that preceded the 

 deposition of the grit, (3) the gradual transgression northward of arenaceous 

 sediments over the eroded folds, the Shawangunk grits being a more south- 

 erly 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 considera- 

 tions 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 Rensselaer grit in the town of 

 Austerlitz, Columbia county. This last named outlier is of especial interest 

 as it lies but 20 miles northeast 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, (Countryman 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 



