120 SIXTEENTH REPORT ON THE CABINET OP NAT. HISTORY. 



formations from Drummond's island and St.Mary's river to the 

 head of Green bay, and thence made a section across the country 

 to the Mississippi river. The position of the sandstone on the 

 St.Marys admitted of no doubt ; and its relative position to the 

 lower limestone had before that time been well determined, and 

 the same was likewise ascertained by the several exploring parties 

 along different lines between Lake Superior and Green bay. 



Throughout Wisconsin, there is no difficulty in recognizing the 

 following sequence : 



Trenton limestone; 

 Black-river or Buff limestone ; 



BiRDSEYE limestone; 



St. Peters sandstone ; 



Lower Magnesian limestone, or Calciferous sandstone ; 



Potsdam sandstone. 



The St.Peters sandstone holds the place of the Chazy limestone 

 of the more eastern localities ; and, with this exception, we have 

 the same sequence that we find in New- York, many of the fossils 

 being common to the limestone of New- York and Wisconsin. 



Dr. Owen, in his published Report, has adopted this view of the 

 sequence, and the explorations of subsequent years have confirmed 

 the opinions then entertained ; and I believe at this time every 

 geologist will admit the identity of the Potsdam sandstone of 

 New- York and the lower sandstone of the Upper Mississippi 

 valley. 



In speaking of this sandstone, I shall, therefore, without hesita- 

 tion, refer to it as the Potsdam sandstone. 



As before remarked, the meagre fauna originally known in this 

 rock in New-York was not sufficient to parallelize it with any 

 European formation, while it was shown to be strongly separated 

 from the next succeeding groups ; but since the discovery of these 

 numerous fossils in the Mississippi valley, there has been no longer 

 any hesitation in recognizing the Potsdam sandstone as equivalent 

 in part, and in parallelism with the Primordial zone so fully 

 established in Bohemia by the researches of M. Barrande. 



These preliminary remarks appear to be necessary ; since, so 

 far as we now know, there are no species of fossils in the western 

 sandstone which are positively identical with those of New- York ; 

 and those geologists who adopt the opinion that identity of species 

 is required to prove equivalency of age in formations, may take 

 exception to the views here advanced. 



