150 PROCEEDINGS OF THE GEOLOGICAL society. [ Dec. 1, 
It is'a more serious objection to the divisions established in New 
York that they are far from being of equal geological importance ; as 
some represent beds distinct both in mineral character and organic 
contents, while others contain nearly the same species of shells and 
have little to distinguish them mineralogically. Thus the Trenton 
and the Hudson River limestones form, according to Mr. Hall, one 
natural zoological group, and in the Western States unite to form the 
blue limestone of Ohio (Hall, Paleontology of New York, p. 61); 
and many of the beds of limestone in the Helderberg series contain 
so nearly the same species throughout, that there would be more 
reason for dividing our mountain limestone into a number of groups 
than there is for separating these. 
This minute subdivision of beds has been indirectly another source 
of error. Many of the American geologists have been strongly 
imbued by the idea, which unfortunately has been promulgated by 
naturalists of eminence in Europe, that different species of animals 
are to be expected m each geological group or formation: and thus 
in multiplymg their stratigraphical divisions they have increased the 
multiplication of supposed species. The result is seen in the great 
number of synonyms im the table of species given farther on, which 
would have been still more numerous if I had had a larger collection 
of specimens to work upon. 
As a first step towards understanding the relative value of the 
American divisions of formations and comparing them with those of 
Europe, I have attempted to classify the New York beds according 
to the distribution of the organic remaims found in them, following 
the ascending order after the example of all the American geologists. 
This may seem a bold attempt from one who has not seen the country 
and can have but limited means at his disposal: but the object to be 
gained is so important as to be worth the risk. With each group of 
beds is given a list of the species of shells which I have found in Mr. 
Lyell’s collection to be identical with those of Europe, or the identity 
of which rests on undoubted authority. I might have increased these 
lists very largely by adding all the supposed identifications of species 
given by the American writers’; but I have rarely availed myself of 
these for the reason already stated, that they appear to be built on 
the comparison of their specimens with our figures and descriptions, 
and not of specimens against specimens. The references to the names 
here used, the synonyms, &e. ., will be found in the general list of 
species given hereafter. 
1. Potsdam Sandstone. 
This is the earliest fossiliferous rock discovered in the United 
States, where it is of considerable importance; it contains Lingule 
and some supposed fucoids. It thus appears that both in America 
and England the Lingule are-among the earliest animal forms yet 
met with, but the species in the two countries are not the same. 
2. Calciferous Sandrock. 
The organic remains in this bed are more varied than in the pre- 
