31 
PALEONTOLOGY OF NEW-YORK. 
A comparison of the species shows that the fossils of the Lower 
Helderberg rocks are analogous to those of the Niagara group, and 
contain among them certain species which we regard as representative 
forms of the Silurian species in Europe; and we cannot do otherwise 
than retain this series as a member of the Silurian system. 
It would seem, therefore, a very natural inference, since the pre¬ 
sence of the Genus Eurypterus is regarded as marking the uppermost 
strata of the Silurian system of Great Britain, that our Lower Helder¬ 
berg group constitutes a series of strata not recognized, and probably 
not existing in the British islands. 
The sequence of these groups, as occurring in the eastern and western 
parts of New-York, and their equivalents in Great Britain, is as fol¬ 
lows in the descending order : 
Eastern New-York, 
Upper Helderberg group, 
Western New-York, 
Upper Helderberg group 
Great Britain, 
— Devonian or Old Red sandstone, 
with fish remains. 
Oriskany sandstone, 
Lower Helderberg group. 
Waterlime group, 
Onondaga-salt group, 
Niagara group, 
Not occurring in Western New-York. 
Waterlime group, 
Onondaga-salt group. 
— Horizon of Lesmahago, with 
Eurypterus. 
Niagara group, 
= Wenlock limestone. 
The relations of these crustacean beds to the earliest Ichthyolite 
beds in Great Britain is very clearly shown by Sir Roderic Murchison, 
with the important conclusions derived therefrom. But while there the 
conditions of the ocean apparently admitted of the direct succession 
of the two faunae, we have in the United States a very strongly marked 
line, which has been traced over more than fifteen hundred miles of out¬ 
crop, with no mingling of material or of the faunae.* 
It is interesting to observe these points of difference in the conditions 
of the two continents, at the time of the distribution and deposition of 
these sediments and the accumulation of calcareous material. These 
discrepancies are moreover suggestive of enquiries as to how far the 
• Notwithstanding this evidence of separation over so wide an area, I am still disposed to believe that 
we may find localities which, from the accumulation of material having been uninterrupted, will show a 
gradual passage fronvone to the other of these formations, if not a mingling of the two faunas. 
