ONONDAGA SALT GROUP. 
139 
In addition to the fossils here enumerated, the Eurypterus lacustris of Harlan is said to 
occur at Williamsville in Erie county. I have not been so fortunate as to meet with it, 
though some fragments of a crustacean have been obtained from that locality. 
Localities of superposition among the rocks of the Onondaga Salt Group, and the next 
succeeding rocks. 
All the sections here presented and other similar ones are constructed from a careful exa¬ 
mination of the rocks, and none are given except where the actual junction of the two groups 
is visible. In some instances much time has been spent in searching for the precise point of 
contact, in order to ascertain whether the change from one rock to another was abrupt, or 
whether it was by gradual intermixture of the superincumbent mass. The object in present¬ 
ing them is to direct those who are examining these rocks to points where the contact of two 
groups can be seen—always a point of interest to the geologist, for there he finds the termi¬ 
nation of a condition of things which gave origin to peculiar forms of animal existence, but 
few of which were continued beyond. 
55 . 
d . Onondaga limestone. 
e. Oriskany sandstone, with concretions, four feet. 
b. Some thin dark layers of impure limestone, representing the Water-lime group—two feet. 
a. Terminal mass of the salt group—used for hydraulic cement. 
Nearly the same order among the strata is to be seen a few miles west of this point. 
The next section shows the order at Tinker’s quarry in West-Mendon, Monroe county. 
56 . 
c. Onondaga limestone, containing numerous coralline fossils, and embracing nodules of chert. 
b. Coarse greenish sandstone or conglomerate, representing the Oriskany sandstone—four inches. 
a. Upper part of Onondaga salt group, exhibiting about twenty-five feet in thin courses of a light ashen color, and entirely 
destitute of fossils. 
18 * 
i 
