166 
HELDERBERG DIVISION. 
igneous injected mass, similar in its formation to a trap dyke, inasmuch as there are no 
appearances of ignition upon the adjacent rock. 
§2. Pentamerus limestone (Plates xx. and viii.). 
This is a gray crystalline limestone, with thick beds from its beginning. Its beds, 
however, are uneven, and some are concretionary and extremely rough ; in fact, as will 
be seen, this concretionary mass is the most persistent and extensive. Its name is derived 
from the great abundance of a fossil called the Pentamerus galeatus (See Vanuxem’s Re¬ 
port, p. 117, fig. 1). It is constant in the rock as far west as Herkimer county; but at its 
extreme western limit, it is rare, if it exist at all. 
Points where this rock may be examined. The most eastern limit of the rock is Becraft’s 
mountain, about three miles southeast of Hudson, on the road to Catskill: it forms two 
or more high bluffs on the east side of the road. Again, west of Catskill, or on the rail¬ 
road between Catskill and Leeds, or on ihe turnpike between the two places. So also it is 
an outcropping mass on the west side of the Hudson river, forming the first of a series of 
cliffs from Kingston point to Coeymans. At numerous places also nearer the main hills of 
the Heidelberg ranges, this rock is constantly present in heavy beds, whose aggregate 
thickness is about thirty feet. Another extensive outcrop of this rock forms the northern 
brow of the Helderberg hills : it exists in cliffs, formed by its outcrop, from Knox to Her¬ 
kimer county, where it begins to lose this character, and to become more depressed. At 
Cherryvalley, at the head of a ravine, it seems to have attained its maximum develop¬ 
ment : from this point westward, it begins to thin out; and when it has reached Manlius, 
Onondaga county, it is only a few feet thick, and destitute of its characteristic fossils or 
other marks except its peculiar concretionary structure. At Tyler Post-office, and at 
Geddes, five miles west of Syracuse, the Onondaga-salt group is in contact with the Onon¬ 
daga limestone, this whole mass having thinned out entirely. 
Uses. This rock is totally unfit for purposes of construction : it is rough, and makes an 
indifferent wall. A part of it forms the cement rock of Ulster county. As a limestone, for 
ordinary purposes, it is not esteemed ; for agricultural purposes, it may be well adapted, 
but has not been tried. 
Range and extent. It will not be difficult to trace this range of limestone, from what has 
been said already. It begins at Becraft’s mountain, near Hudson ; forms one of the highest 
outcropping rocks in the first tier of hills which bound the Hudson valley west, from Coey¬ 
mans to Kingston, and thence from Kingston to the falls of the Rondout. The same may 
be traced from Coeymans west to Manlius, and disappears entirely a few miles west of 
Manlius. The belt it forms is every where inconsiderable, and would be more properly 
represented by an outcropping edge. 
Relations and connection of the Pentamerus limestone. Below, every where in New-York, 
it is succeeded by that part of the Onondaga-salt group which is called the Manlius water- 
limes. Above, and at the east, it is succeeded by the Catskill shaly limestone. Near its 
