I6O NEW YORK STATE MUSEUM 



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 facies. In favor of this view it may 

 be said that both formations rest on the same basis (Cambric and Lower 

 Siluric slate) and that on account of the rising of the Taconic mountains in 

 early Siluric time, there may have existed a littoral facies of the Helderberg 

 rocks to the east. But this view is strongly opposed by the fact that the 

 Helderberg rocks do not show any indications of approach to a littoral 

 region at Becraft mountain, but retain the same lithologic characters 

 over a vast area. There would hence have to be assumed an extremely 

 abrupt and improbable change in facies in the short distance of 20 miles 

 from Becraft mountain to the outlier at Austerlitz. A somewhat different 

 case is presented by the Oriskany sandstone, Esopus grit and Schoharie 

 grit which in some places, as at Whiteport and Kingston, contain conglom- 

 erate beds. It is altogether probable that the material of these conglom- 

 erates was derived from the south and the Oriskany sandstone is too thin a 

 layer (30 feet) at Becraft mountain, to be correlated with the thick mass 

 of the Rensselaer grit (1400 feet). It is, however, possible that the Esopus 

 and Schoharie grits which at Becraft mountain have a combined thickness 

 of 300 feet and are similarly barren in fossils, once continued northeastward 

 into the Rensselaer grit trough. It must further be considered that the 

 Rensselaer grit plateau represents a deposit in a long submeridional 

 Appalachian trough. Its pebbles of coarse and fine gneiss came from a 

 short distance and the numerous Lower Cambric pebbles probably from 

 places north of the plateau. Its deposits suggest those of an embayment 

 receiving its materials from the north. The entire absence of the fossils 

 occurring in the nearby Becraft mountain formations favors this conception 

 of estuarine conditions. 



The evidence compels us to grant that the Rensselaer grit is of later 

 than Siluric age ; there is some good reason for regarding it an eastern 

 deposit contemporary with the early Devonic, but the alternative proposi- 

 tion stands open, that its estuarine character and great thickness suggest 



