viii 
PREFACE. 
In Eastern New-York, the coarser sediments of the Hamilton group 
present proportionally few Brachiopoda ; and in some localities are com¬ 
paratively barren of all fossils. The Lamellibranchiata, which are the 
characteristic fossils of the coarser sediments of this group, gradually 
diminish in number as the finer materials supervene, and the addition 
of a larger proportion of calcareous matter is accompanied by the advent 
of great numbers of Brachiopoda, together with Corals and other fossils 
which are unknown in the eastern part of the State. So great is this 
change, that were a collection of fossils from the Hamilton group in the 
counties of Albany and Schoharie to be compared with a collection from 
the same group in Genesee and Erie counties, the number of species com¬ 
mon to both would be less than has been sometimes indicated as passing 
from one geological formation to another. 
The same conditions hold true in a more marked degree in the Che¬ 
mung group, which, in the counties bordering the Hudson river, is 
nearly destitute of animal fossils, but contain many plant remains. 
Farther to the westward, a few lamellibranchiates and brachiopods 
appear, and their number constantly increases to the central counties of 
the State, beyond which the Brachiopoda greatly predominate over all 
the other organisms. Nor is this all ; not only do the Brachiopoda 
increase in number of species and of individuals, but the species are 
almost entirely distinct from those in the more eastern localities of the 
group. We notice, moreover, that in these western localities within the 
State the prevailing fossils present a “carboniferous aspect,” or are of 
generic and specific forms much resembling the prevailing fossils of the 
acknowledged Carboniferous rocks of the West. We find also among them 
a few forms which might readily be mistaken for Carboniferous species ; 
and in one or two instances, there is scarcely room for specific separa¬ 
tion. Here again, in a more emphatic sense, do we find the fauna of the 
same physical group of strata so entirely unlike at points three hundred 
miles distant, that there are probably no identical species. At the same 
time, the entire Chemung fauna of the western counties of New-York 
presents more analogy with the fauna of the so-called Carboniferous 
