HELDERBERG DIVISION. 
325 
quence of being nearly horizontal, forms almost the only rock over large tracts of country • 
but in the Helderberg mountains, and on the eastern and southeastern outcrop of the strata, 
the whole series can be examined within a very short distance, and the superposition of nearly 
all the rocks of this series may be seen by following up the ravines. In consequence of these 
rocks being so well developed on the Helderberg mountains, and their forming a natural 
group, strongly marked in their lithological and palaeontological characters from the strata 
lying above and below them, the term of Helderberg division is used to designate them. 
Mr. Vanuxem has, very properly in my view, divided this division into several groups, to 
which he has given particular names, indicative of localities where they can be examined 
easily, or where they are most largely developed, or best characterized by their lithological 
characters or organic contents, or peculiar fossils. 
Some of the rocks that are largely developed in masses of great thickness and extent in the 
central and western parts of the State, and the position of which is such in the order of suc¬ 
cession as to place them within the limits of the series under consideration, diminish in thick¬ 
ness from west to east, so as to have wedged out and entirely disappeared, or to be very thin, 
and not to be found except by careful investigation. Again, there are others well developed 
in the east part of the State, that gradually thin out and disappear as we trace them to the 
west. I am disposed to adopt the names that Prof. Vanuxem has proposed for the rocks em¬ 
braced within the limits of this series in the First Geological District, as subordinate members 
of a great natural group, and which is seen to such advantage, well developed in the Hel¬ 
derberg mountains in Albany and Schoharie counties, and to which the name of Helderberg 
division is now applied. 
The following are the principal masses of the Helderberg division in their order of super¬ 
position. 
Members. 
Synonimes. 
Corniferous limestone. 
Onondaga limestone. 
Schoharie grit. 
Cauda-galli grit. 
Oriskany sandstone. 
Delthyris shaly limestone. 
Seneca limestone, Selenurus limestone of Gebhard. 
Grey sparry limestone. 
Schoharie layers, Shell grit. 
Cocktail grit of Dr. Eights. 
White sandstone of 1838, No. 7 of Pennsylvania r^ort. 
C Scutella Umestone, Sparry limestone of Gehhard, Delthyris shales, Catskill 
\ shaly limestone. 
No. 6 of the Pennsylvania survey. 
TentacuUte limestone, Water limestone. Hydraulic limerock of Eaton. 
The following section was given by Mr. J. G. Gebhard junior, but the above is believed to 
be most aecuirate from^ repeated observation. 
1. Grey calcareous sandstone, abounding with fossils. 
2. Corniferous limestone, containing many layers and courses of nodules of chert and hornstone. 
3. Cocktail grit of Dr. Eights, characterized by Fucoides cauda-galli. 
