FIFTH REPORT OF THE DIRECTOR I908 



33 



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 Helder- 

 berg- 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 that they possess 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 dif- 

 ferent cause is presented by the Oriskany sandstone, Esopus grit 

 and Schoharie grit which not only contain sand and grit at 

 Becraft mountain and in the Helderbergs, but in some places, as at 

 Whiteport and Kingston, contain conglomerate beds. It is alto- 

 gether probable that the material of these conglomerates 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. Since they represent an invasion of the sea that came from 

 the south and spread northward in the direction of the Rensselaer 

 grit plateau, and the overlapping Rensselaer grit is clearly the 

 product of an invading, not a receding, sea, it is a reasonable propo- 

 sition that the Rensselaer grit was deposited in a long narrow 

 embayment extending northward from the Oriskany-Esopus- 

 Schoharie grit sea of southern New York. But in this case also, 

 there is still to be explained the extremely rapid change from the 

 typical Esopus grit of Becraft mountain to the red and green 

 slates and coarse grits of the Austerlitz outlier, and the fact that the 

 Esopus grit is thicker southward (700 feet in Orange county), and 

 thins out toward Becraft mountain. The regular succession of the 

 various members of the Lower and Middle Devonic in Becraft 

 mountain with the same lithologic characters as in the Helderbergs 

 and much farther west and south is in itself cumulative evidence 

 that the Helderberg sea extended farther east than the present 

 Rensselaer plateau and with unchanged or but little changed 

 conditions. 



It must further be considered that the Rensselaer grit plateau 



