178 



HELDERBERG DIVISION. 



Table exhibiting the thickness of the rocks conijwsing the Helderberg division, at different places in the 



State of JVew- York. 



NAMES OF ROCKS. 



Red shale 



Green shale, gypseous rock &, watcrlime, 



Pentamerus limestone 



Delthyris shaly limestone 



Encrinal limestone 



Upper Pentamerus limestone .... 



Oriskany Sandstone 



Cauda-galli g:it 



Schoharie grit 



OnoQdaga and Corniferous limestone 



TAe Onondaga limestone, the superior rock of the Helderberg division. The importance 

 of this rock is seen in another and different point of view, namely, in forming a distinct 

 line of demarkation between two divisions of rocks, which, though intended only as geo- 

 graphical lines in this instance at least, yet really defines the end of a series in tlie system. 

 Lithologically the end of the series with this rock is indicated, though it could not be 

 proved. If, however, organic bodies are permitted to speak, they tell us that such is the 

 fact ; for it is rare that those of this rock go up into the succeeding deposits, and still less 

 probable is it that any of the rocks below the Onondaga limestone reach the shales and 

 sandstones of the Erie division. This rock, then, forms or marks an era in the New- 

 York system, which must always be regarded as important ; and this is true, in whatever 

 light we may regard this system ; or whatever classification we may adopt, this rock must 

 form the termination of one of the divisions. It is true that the upper portions are dark 

 colored, and the layers are separated by seams of sliale ; still this only proves that the 

 change which was about to take place was not sudden or immediate, but gradual. It is 

 probable the dark color of much of the upper part of the Corniferous limestone is of the 

 same nature as that of (he Marcellus slate, the mass which reposes upon it. 



On referring to wliat is said in the closing remarks upon the Champlain division, it will 

 now be seen thnt we have at least two very satisfactory divisions in the New-York system : 

 the first, ending with tlic gray sandstone of the Champlain division ; and the second, with 

 the Onondaga limestone. Between the lower division and the next succeeding, the On- 

 tario division, the affinity or resemblance is only slight. There is, however, a greater 

 resemblance between the Helderberg division and the Erie, probably, than between the 



