WATERLIME GROUP. 
JS8 7 
Although found in a loose fragment of limestone, the character of the 
rock and the associated fossils are conclusive in regard to its geological 
position. 
These peculiar organisms, found thus between the Onondaga-salt group 
below and the Lower Helderberg group above, I have referred rather to 
the former; for wdiile the occurrence of the single carapace of a species 
of Eurypterus, associated with known fossils of the Tentaculite limestone, 
allies the formation in some measure with the rocks above, its lithological 
associations are altogether with the rocks below. 
The sequence of strata above given shows conclusively that the Eury¬ 
pterus beds are not to be regarded as of Devonian age. The rocks of the 
Lower Helderberg are admitted to be Silurian; and while no one would 
include in the Devonian period rocks below the Oriskany sandstone, this, 
from its mingling of species, may be regarded as debatable ground. The 
Eurypterus (with a single exception) lies therefore between the Niagara 
and Lower Helderberg groups, in strata above those containing the fossils 
represented in the second volume of the Palaeontology of New-York, and 
below those containing the fossils represented on the first seventy-nine 
plates of the present volume*. 
It seems scarcely necessary, therefore, to discuss the question of the 
age of the strata containing the Eurypterus; and I introduce these re¬ 
marks to correct the erroneous reference frequently made of these fossils 
to the Devonian system. 
In comparing the rocks of this country with those of Europe, we learn 
from the investigations of Sir Roderick Murchison that he has always 
found the strata characterized by these crustaceans immediately to under¬ 
lie the rocks of undoubted Devonian age. This eminent geologist remarks: 
* The Eurypterus should indeed more properly have formed the concluding part of the second volume 
of the Palaeontology of New-York; but at that time the collections possessed by me, or known to exist 
in the State, were too meagre to afford means for a proper illustration of the species, and much less for 
adding to our knowledge of the structure of the animal. The descriptions were accordingly postponed to 
the third volume, and are placed at the end of the Crustacea, not as indicating their geological relations, 
but as,a distinct group to be studied by themselves; while their geological place, in reference to the fossils 
of this volume, would precede those of the first plates. 
