380 Di', Hunt on the Primordial Zone 



Vermont, which is supposed to overlie the black slates in question. 

 As this primordial genus occurs also in the Potsdam sandstone of 

 Lake Champlain, the question arises whether these slates are 

 palseontologically distinct from the Potsdam, or are only its deep 

 sea equivalent, sustaining to the littoral formation of quartzose 

 sandstone on Lake Champlain, the same relation as the great 

 Quebec group does to the Calciferous sandrock of the New York 

 geologists. Dr. Emmons claims that the whole of his Taconic 

 system is inferior to the Potsdam sandstone, which is the admit- 

 ted base of the Champlain division, but we have already shown 

 that the whole of his system, with the probable exception of 

 these slates, is of the age of the Calciferous sandrock, the second 

 member of that division. Unless then these lower black slates 

 contain a fauna distinct from and older than that of the Potsdam 

 sandstone, there remains absolutely nothing of the Taconic system 

 which Dr. Emmons placed below the base of the Champlain divi- 

 sion, that is to say, below the Potsdam sandstone. If, however, 

 as is probable, these slates contain a fauna distinct from the Pots- 

 dam, they might be retained under the name of the Taconic form- 

 ation, as a lower member of the Primordial Zone, to which the 

 Potsdam sandstone unquestionably belongs. 



These lower slates in Georgia, Vermont,have as already remarked 

 furnished certain trilobites of primordial type which Mr.James Hall 

 has described under the name of Oleniis Vcrmontana and Olenus 

 Thompsoni, though they are provisionally referred by Barrande 

 io\hQ gQ\\\\?> Paradoxides. In the meantime the only trilobite as yet 

 met with in the typical Potsdam sandstone of this region, which is 

 rarely fossiliferous, is Conocephalites.* A collection of fossils re- 

 cently made by Mr. James Richardson in exploring the Straits 

 of Bellisle for the Geological Survey of Canada, fortunately 

 furnishes the means of determining the relations of the tri- 

 lobites described bv Mr. Hall. On the north side of the 

 Straits he found reposing on the Laurentian rocks a coarse 

 reddish sandstone holding Scolithus like that from the Primal 

 sandstone of Pennsylvania. Resting upon this, and dipping 

 gently southward, is a limestone in which occur both Olenus 



* Mr. Barrande refers to three species of Dikellocepaalus indicated by 

 Dr. Bigsby as occurring in the Potsdam of New York. It will be seen 

 by referring to his memoir (Quar. Jour. Geol, Soc. 1858, p. 339, com- 

 pared with p. 420,) that Dr. B. alludes only to the existence of these 

 species as described by Owen in the Mississippi valley. 



