54 NEW YORK STATE MUSEUM 



Medina sedimentation. The recent work of C. A. Hartnagel as 

 published in these reports indicates conclusively that in the typical 

 section the Oneida conglomerate is not a formational imit but 

 actually lies within the Medina sandstones, that further the Shawan- 

 gunk grit on stratigraphic evidence alone, is of an age much 

 later than the Medina formation and being overlain conform- 

 ably by rocks of Postsalina age is probably the eastern representa- 

 tive of the Salina deposition. The essential confirmation of the 

 latter conclusion by the discovery of an eurypterid fauna in the 

 Shawangunk grit is elsewhere referred to. Mr Hartnagel has 

 pointed out the improbability of the Siluric age of the Rensselaer 

 grit or of its equivalence with the Medina-Oneida sediments, his 

 chief arguments being (i) the extensive gap by nondeposition 

 between the eastern terminus of the Oneida conglomerate in 

 Herkimer county and the Rensselaer grit plateau, (2) the long time 

 interval that must be postulated 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 grit being a more southerly and 

 hence earlier representative of such transgression. The region has 

 been carefully searched during the past season for some evidence 

 of fossils which would throw definite light on the problem of the age 

 of this Rensselaer grit, but though this evidence still fails and 

 can not be explained by secondary changes of the rocks, the strati- 

 graphic considerations indicate the propriety of assigning to this 

 formation a distinctly later age. 



No beds later than Trenton age have been observed near the 

 edge of the plateau and there are apparently no outliers to bridge 

 the gap between the late Siluric and early Devonic rocks of Becraft 

 mountain, Mt Bob and the last outlier of the Rensselaer grit in 

 the town of Austerlitz, Columbia co. This last outlier is of especial 

 interest because it lies but 20 miles northeast of Becraft mountain 

 and is situated a considerable distance south of the main mass of 

 the Rensselaer grit plateau. For these reasons it was specially 

 studied but found to be in no way lithologically different from the 

 Rensselaer grit in Rensselaer county and containing the same alter- 

 nations 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 Helderbergs near Albany, (Coun- 

 tryman hill) — the two places where the deposits of the Siluro- 

 Devonic basin of New York approach nearest to the Rensselaer 



