324 
GEOLOGY OF THE FIRST DISTRICT. 
III. HELDERBERG DIVISION. 
This division embraces a series of limestones, varied in mineralogical character, in chemical 
composition, and abounds in fossil remains. It contains subordinate beds of shales, slates 
and siliceous grits. It skirts the group of rocks last described, in a parallel zone, and under¬ 
lies them, it is supposed, through their whole extent. 
This formation extends in the district under examination, from Sharon springs in Schoharie 
county, by Schoharie, to the northeast part of the Helderberg mountains ; thence southeast, 
to near New-Baltimore ; thence southwardly, by Catskill and Saugerties, to Rondout; thence 
up the valley of the Rondout, by Rochester, Wawarsing and Ellenville ; thence on through 
the Mamakating valley, by Cuddebackville, to Carpenter’s point on the Delaware. At the 
latter place, it passes out of the State of New-York into New-Jersey, and crosses the Dela¬ 
ware into Pennsylvania, at the Walpack bend of the Delaware, according to Prof. Rogers.* 
Becraft’s mountain near Hudson, and Mount Bob, a few miles to the northeast, are outliers 
of this division. 
This formation varies much in its subordinate beds in different localities, particular .beds 
being either entirely wanting, or replaced by others ; but its fossil contents are nearly uniform. 
Mr. J. G. Gebhard junior, of Schoharie, who was the assistant for Schoharie county, has exa¬ 
mined this group with much attention for several years, and he has a more perfect collection 
cf the fossil remains of its various strata than any other individual. 
The lower strata of this division of rocks consist of various beds of common and hydraulic 
limestones, varying much in thickness and in quality, even in contiguous quarries. These 
strata sometimes rest unconformably upon the Hudson slates, as at Lawrence’s quarry on the 
Rondout, opposite Wilbur ; sometimes conformably on the Shawangunk grit, (Millstone grit 
of Eaton,) as at Rosendale and Lawrenceville on the Rondout; sometimes on the red and 
variegated shales and grits that overlie the Shawangunk grits, as at the High falls of the Ron¬ 
dout, in Marbletown; and upon the shales and grits of Schenectady and the north part of 
Schoharie county (Hudson slate). These facts and others connected with the superposition 
and derangements of the Helderberg division are illustrated in PI. 26 ; Figs. 3, 4, 5 and 6 of 
PL 25 ; Figs. 4, 5, 6 of PI. 24; Fig. 1 of PL 12; Fig. 15 of PL 9; Figs. 1, 2, 3, 4, 5, 6, 
7, 8, 9, 10 of PL 8 ; Figs. 1. 2, 3, 4, 5, 6, 9 of PL 7; Fig. 7 of PL 6 ; Figs. 2, 3, of PL 39; 
Figs. 14 of PL 38; Figs. 8, 9 of PL 27. 
The rocks of this division form a mass of some four hundred feet in thickness, composed of 
various strata of limestone, each characterized by its fossils and mineralogical characters, and 
interstratified with shales and grits ; but limestone is the predominating rock. The rocks of 
this series occupy a great area in the central part of the State ; and each stratum, in conse- 
* Vide Prof. Rodgers’ Second Annual Report on the Geological Survey of Pennsylvania, p. 56. 
