INTRODUCTION. S 



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 forra.s. 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 himdred miles distant 

 from each other. 



In the table accompanying the first volume of the PaljBontology 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 rolume is a specimen, the locality of which is uncertain. 



