350 
GEOLOGY OF THE FIRST DISTRICT. 
of the rocks of the Helderberg division. From Coeymans, by Bethlehem, Bern, Schoharie, 
Cobleskill, Carlisle and Sharon, into the Third district, the rock has a gentle dip to the west 
and south, cropping out towards the Hudson and Mohawk valleys, ' with a mural escarpment 
or a steep acclivity. 
The thickness of this group of rock varies from fifty to one hundred and fifty or two hun¬ 
dred feet, in different localities, usually from one hundred to one hundred and fifty feet. 
The group is composed of two principal members, viz. the | Water\Tmes?o?e°;^^’ ^ 
each of which might with propriety be subdivided, in consequence of the marked difference 
of the zoological and lithological characters of the subdivisions. 
The upper part of the tentaculite limestone is a black and dark grey slaty compact (in some 
layers subcrystalline) limestone, in layers from an inch to a foot thick, and contains several 
species of the Asaphus and Calymene. 
The middle part of the tentaculite limestone is composed of slaty black layers of compact 
limestone, containing an abundance of the Tentaculites ornatus, Cytherina alia, Orthis pli- 
cata, and some of the Avicula rugosa. These are characteristic fossils. 
The lower part is also composed of black and dark grey compact and subcrystalline lime¬ 
stones, abounding in the remains of radiata, mostly favosites, columnaria, catenipora, etc. 
The water limestones with interstratified masses of common limestone, underlie the above. 
The detailed section opposite Wilbur (Vide page 331 of this Report) shows the alternation and 
relative thicknesses of the different masses. Tuhipora catenulata, a coralline like Cateni¬ 
pora escharoides, and some other fossils, occur in the locality of that section and some other 
places, but they are rare. 
In some places, one of the beds of the Water-lime group is geodiferous, and contains beauti¬ 
ful crystals of calc spar, and crystalline compounds containing baryta, strontia and lime, mi¬ 
nerals that are or will be described in the Mineralogical Report by Prof. Beck. At Schoharie, 
a stratum of about eight feet in thickness at the base of the Water-lime series of dark colored 
compact limestone, contains great numbers of globular masses of a species of favosite. Many 
of these have been polished by Mr. John S. Bonny, and distributed in various parts of the 
country in exchanges of fossils and mineral specimens. They take a high polish, and the 
sections through the globular and ovoidal masses exhibit sections across and through the 
columns in all directions, so as to develop the whole structure of the fossil. 
A large conical univalve was found in this stratum of limestone at the base of the Water- 
lime series, immediately above the green pyritous underlying shales at Schoharie, by Mr. Geb- 
hard, who has made a drawing of it. A single specimen only has been found. Plate 20 of 
this volume represents this fossil. 
Localities out of the general range of the Helderberg division. 
“A limestone, containing abundance of fossils, like those of the middle limestone of Be-, 
craft’s mountain, is found in the town of Cornwall, two and a half miles west of the village 
