300 INDEX TO THE STRATIGRAPHY OF NORTH AMERICA. 



as shown by recent analyses, that they may be wisely regarded as indicating the passage of the 

 earUer into the later fauna. 



The Helderbergian rocks (in the Helderberg Mountain region comprising the following 

 divisions from below upward: (1) Coeymans limestone, (2) New Scotland limestone and shale, 

 (3) Becraft limestone) enter New York from the southeast along the New York-New Jersey line 

 and end northward in an abrupt escarpment facing east and north in the southern angle of the 

 present Hudson and Mohawk rivers. Of this heavy sheet of calcareous strata there is no trace 

 in New York east of the Hudson River save two small synclinal outliers in Columbia County, 

 Becraft Mountain and Mount Bob. As the formation progresses northward from its entry into 

 the State its thickness increases to where it is abruptly cut off in an erect wall. The Helderberg 

 escarpment carries in its very topography the evidence of a former wide extension on toward 

 the east and northeast. The continuation of this formation westward in New York is notable 

 for its rapid thinning and quick disappearance. The subdivision at the Helderberg Mountain 

 is soon lost westward. The lower division or Coeymans limestone appears to be that extending 

 farthest, as far as the eastern limits of Onondaga County, but the narrow east and west extent 

 of the Helderberg sea is shown by the entire absence of the higher divisions far west of Schoharie 



Creek. 



The Oriskany period succeeding was a time of transgression over the Helderberg deposits 

 beneath. Then the northern coast line in western New York was broken and embayed. While 

 calcareous deposits were formed in the deeper water of the southern reaches, the shore deposits 

 of sand extended westward to Buffalo, in part over eroded surfaces of SUuric limestones to which 

 the Helderbergian sediments had not extended. We have had occasion to show that from the 

 Helderberg westward the sandy shoal-water deposits of this Oriskany time are lenses and thin 

 sheets, often disconnected, in some places rising to considerable thicknesses of friable quartz shore 

 sand into which the waters have roUed the organic remains of the outer sea. These lenses we 

 conceive were separated by tongues of land dividing the embayments of the shore line. The 

 Oriskany in our view presents in New York a twofold facies, that of the deeper littoral repre- 

 sented by the calcareous deposits from the Helderberg southward to Port Jervis and that 

 of the shallow littoral from Schoharie westward ; yet it is quite possible that the latter deposits 

 are of later date than most of the former and represent the final transgression of shore sands 

 over the sinking land of Helderbergian time. 



The Oriskany sandstone is succeeded by the Esopus shale, which is described 

 by Darton.^^" The Esopus is said to be "in greater part a fine-grained arenaceous 

 deposit of dark-gray color." 



About Schoharie and westward to its termination it is a moderately hard sandy shale varying 

 in color from dark gray or buff to light oUve, but east and south with increasing thickness the 

 color becomes darker, the texture of the rock is harder, and slaty cleavage is general. * * * 



The formation has a thickness of 110 feet at ClarksvUle. 



I 



The Ulsterian of the New York State Survey comprises, in addition to the 

 Esopus shale; a locally developed but not extensive formation known as the Schoharie 

 grit and the widespread Onondaga limestone. 



Darton ^^ describes these formations, together with others of the Helderberg 

 Mountains. 



The Schoharie grit is a local deposit which is characteristically developed near 

 Schoharie and extends through Schoharie and Albany counties to Ulster County. It 

 is a very -arenaceous, limestone which merges into the Onondaga above but is more 

 sharply separated from the underlying formation. It is locally absent and the 

 Onondaga then rests on the Esopus shale. 



