INTRODUCTION. 
3 
permeated by silica, which has had the effect in many instances of nearly 
obliterating the organic bodies. In Central New-York, the porous character 
of this sandstone, with its numerous small irregular cavities, often lined 
or filled with quartz crystals, or permeated by siliceous veins, has left the 
fossils in an obscure and imperfect condition. 
In addition to the instances in Canada, we have some evidence that this • 
formation is fossiliferous in its more northerly extension at the west; 
since a piece of the rock found upon the Menominee river was completely 
filled with fragments of fossils, principally of trilobites. In this example, 
the rock is highly calcareous, with a distinct intermingling of grains of 
sand, but containing no cherty matter or seams of silica, and is entirely 
free from the small cavities so common in this rock elsewhere. 
Farther to the south, in the State of Missouri, the Calciferous sandstone 
contains numerous fossils, bearing the general character of those given in 
the first volume of the Palaeontology of New-York; while many are of 
distinct specific forms. The extensive outcrop of this rock in Missouri, 
connected with the fact that it is there also the lead-bearing rock, give 
great facilities for exploration; and we shall soon have the means of 
knowing more fully the nature of the fauna of this ancient formation, both 
in Canada and Missouri, at points more than twelve hundred miles distant 
from each other. 
In the table accompanying the first volume of the Palaeontology of 
New-York, showing the vertical range of the fossils in the different groups, 
all those of the Potsdam sandstone and Calciferous sandstone were found 
to be restricted in their geological range to these rocks*. Although a 
meagre fauna, as there presented, it nevertheless furnished presumptive 
evidence in favor of uniting these formations as a single group. All sub¬ 
sequent investigations have corroborated the previous facts, and sustain 
this view of the relations of these two rocks, and their distinction from 
the groups above. Between these lower beds and the succeeding rocks, 
* The single exception indicated in the volume is a specimen, the locality of which is uncertain. 
