108 
PALiEONTOLOGY OF NEW-YORS. 
a group so uniform and well characterised as that of Niagara. As I have already shown, the 
almost total absence of calcareous matter has precluded the existence of nearly all those forms 
of fossils peculiar to the Niagara group ; and the shales, sandstones, and conglomeritic layers, 
are marked by the presence of an infinite-number and variety of marine plants, with few 
molluscs, and here and there a fragment of a trilobite of the same species as those in the 
Niagara group. Even here we perceive, notwithstanding the discordant nature of the materials 
of the two groups, that they belong to a period during which the same fauna to some extent 
existed. Although the Homalonotus, Phacops and Bumastis occur in the shaly sandstones of 
the lower part of the group in Oneida county, they could not exist in any considerable num¬ 
bers, or degree of development, on account of the nature and the conditions of the sediment. 
In addition to the influences of the prevailing siliceous and argillaceous character of the 
strata of this group in the eastern and central portions of this State, we have that of the ores 
of iron, which, in all situations, appear to be prejudicial to most forms of animal life ; and 
though these ore beds are apparently made up of organic exuviae, yet fossils are comparatively 
rare in their immediate neighborhood, or where the hydrate of iron enters into the composi¬ 
tion of the surrounding strata. 
I have presented all these facts, that they may be considered in reference to the period from 
which the fossils are described. Notwithstanding the dissimilar character of the groups in some 
places, yet regarding their entire extent and character, I am inclined to unite them as one 
group ; but since they have heretofore been separated and thus published in the Geological 
Reports, I have preferred to leave the determination of the question to a future time, giving 
the fossils of each group by themselves, indicating those which are common to both. In order, 
however, not too widely to separate some of the families, I have carried forward the Crinoidea 
and Trilobites to be described with those of the Niagara group ; and I should have done the 
same with the Corals, had they not been already included in the numbering of the preceding 
plates. 
Regarding the very great advantages to be derived from a minute subdivision among the 
groups, I am unwilling to describe in conjunction, or as from the same group, fossils that are 
in a great degree restricted to individual rocks or beds of such group, where it is composed 
of several members. It is far more easy for the student to unite these, than it would be to 
separate them ; and to those who look at their entire character for the purpose of generalizing 
these subdivisions, it can offer ho objection that they are presented in the order of their oc¬ 
currence, the true order of their appearance or coming into existence upon our planet. This 
must be my only apology with those who think that the science is retarded by numerous sub¬ 
divisions, but which appear to me, on the other hand, to facilitate progress, by giving us 
more exact knowledge for the basis of our generalizations. 
