Contributions to Palaeontology. 



95 



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 

 hesitation, 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 

 exceptions to the views here advanced. 



With the hope of adding to our knowledge of the 

 primordial fauna of the northwest, I have, with much 

 labor, selected from very extensive collections of trilobitic 

 remains made at intervals from 1850 to 1859, all that 

 appeared to me of sufficient importance to be illustrated. 

 In a friable sandstone with no vestige of the crust re- 

 maining, these fossils offer very unsatisfactory material 

 for investigation. It is, however, apparently impossible to 

 obtain better specimens ; for in all the localities examined, 



