INTRODUCTION. 9S 



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 aflfinities 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 be 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, Avhich will 

 establish the full value of this group in the sequence of formations and 

 faunae 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 Palteontology of New-York, Vol. ii. 

 [ PALi«ONTOLOOT III.] 4 



