INTRODUCTION. 
95 
new species of fossils; and we may very justly conclude that between 
the Hudson and Mississippi rivers, in the parallel of New-York, no means 
exist for developing new conclusions of importance regarding this group 
of strata, which holds a very marked position between the true Lower 
Silurian and Upper Silurian strata, according to the divisions recognized 
in Great Britain*. 
In tracing the Clinton group westerly, we find its affinities more with 
the rocks below, or that the material and fossils recognized on the one 
side as the Clinton formation are not strongly separated from the upper 
beds of the Hudson-river group; and studied in these localities alone, they 
might he regarded as constituting part of the same. On the other hand, the 
Niagara becomes defined as a calcareous group, and the line between it and 
the strata below is strongly drawn. The base of this limestone would every¬ 
where be recognized as the base of the Upper Silurian rocks, while the 
strata below are marked by fossils which belong to the Lower Silurian fauna. 
Much light has been thrown upon the history of these intermediate 
formations by the investigations before alluded to, in the island of Anti¬ 
costi. It has been shown that the sediments of this period have been 
there deposited on a more extensive scale, and in a degree of completeness 
unknown elsewhere, while the fauna rises to the rank of that of the pre¬ 
ceding or succeeding periods : therefore we are to look to developments in 
the northeast for an exposition of the facts and phenomena, which will 
establish the full value of this group in the sequence of formations and 
faunee of the palaeozoic times. 
It is among the middle Silurian rocks of that region that we have more 
additions to our previous knowledge, than in any other among the older 
palaeozoic formations. The very critical and elaborate investigations in the 
Geological Survey of Canada, carried on in localities, as we shall observe, 
nearer to the source of the sedimentary formations, and over a very wide 
area, promise results of the highest interest in investigations of strata 
which, to the west and southwest, gradually attenuate and finally disappear. 
* See Palaeontology of New-York, Vol. ii. 
[ Palaeontology III.] 
4 
