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NEW YORK STATE MUSEUM 



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 Siluric 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 rolled the organic remains of the outer sea. These 

 lenses we conceive were separated by tongues of land dividing the embay- 

 ments of the shore line. The Oriskany in our view presents in New York 

 a twofold facies, that of the deeper littoral represented by the calcareous 

 deposits from the Helderberg southward to Port Jervis and that of the 

 shallow littoral from Schoharie westward ; yet it is quite probable 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 Helderberg sea in New York 



