HELDERBERG DIVISION. 
167 
western terminus at Manlius, it is succeeded by the Onondaga limestone, the rocks which 
interpose at the east between it and the onondaga in the valley of the Hudson being dis¬ 
continued (See PI. XX. Main section 1 ; also sections 2 and 5). 
Disturbances which the Pentamcrus limestone has suffered. It is principally in the valley 
of the Rondout that this rock has been disturbed to the greatest extent, in common with 
its associates. Upon Catskill creek, three miles west of the village of Catskill, near the 
railroad, the rock is not only elevated, but curved as represented in PI. IV., forming an 
interesting and rather picturesque view. The effect is due to lateral pressure and the joint 
operation of an elevating force, which has fractured this thick rock, and separated it from 
its continuity. It appears in the face of a precipice 250 - 300 feet high. The exposed 
rock at the top of the eminence is the Pentamerus limestone. 
Terrace and outcrop of the Water and Pentamerus limestones , as they appear in the Schoharie 
range (PI. viii.). The semi-panoramic view in Plate 8 gives a better idea of the outcropping 
rocks, of the Helderberg, than can be conveyed by description alone. The series of rocks 
in this plate are the same as those of PI. I. of the Helderberg range, except that the Old 
Red sandstone does not occur within the field of view. The naked perpendicular cliffs are 
formed of the pentamerus, which is the superior and prominent rock, and the thin-bedded 
waterlimes which are directly beneath. The superior masses are the Onondaga limestone 
and Marcellus shales; the inferior, the thick-bedded Hudson-river series, which extends 
north to the valley of the Mohawk. 
§ 3. Delthyris shaly limestone (PI. xx. Sec. 1). 
The passage of the Pentamerus limestone into the Delthyris shaly limestone is rather 
abrupt or indistinct. The entire mass of the shaly limestone is argillaceous ; some layers 
consisting of slate, which disintegrate : others resist the action of the weather for a long 
time, and are extremely tough and difficult to break ; they all, however, become drab- 
colored externally on exposure to the weather, while internally they retain a bluish color. 
The grain is fine, and unlike the pentamerus ; in fact, the harder layers are nearly com¬ 
pact. The limestone throughout is impure, mixed witli argillaceous matter and silex, 
and for this reason it is unfit for lime. It is useless too as a flagging stone, and is only 
good for stone fences. 
Distinctive characters. It is not difficult to distinguish this rock from the preceding lime¬ 
stones, when once we have become familiar with its aspect; still, the best characters are 
derived from its fossils. Several species of Delthyris are confined to it (See Vanuxem’s 
Report, p. 120, and p. 122 for figures of a few of its characteristic fossils). 
Extent and limits of the Delthyris shaly limestone. It requires to be traced in a line, as, 
with the exception of one or two limited patches, it appears only in an outcropping edge. 
At Becraft’s mountain it is one of the principal rocks : this is its eastern limit. It forms 
a north and south outcropping edge near the west side of the Hudson, from Kingston point 
to Coeymans ; and from thence west, it accompanies the Pentamerus limestone as far as 
