420 



vival in this connection of the Taconic system of Prof. Emmons. 

 He expressed the highest admiration for the labors of M. Bar- 

 rande in paleozoic geology, but felt sure that a more complete 

 knowledge of the conditions in which our lower fossiliferous rocks 

 occur would lead him to a different conclusion. 



In considering this subject, it is important to bear in mind that 

 no question is made as to the existence in this country of what 

 M. Barrande would designate as his primordial series. This is 

 already recognized in the Potsdam or Primal group of our Ameri- 

 can geology. But the evidence of observations covering the 

 whole margin of the Appalachians, and ranging through Canada, 

 the Northwestern States, and the prolonged outcrop in the Black 

 Hills and Rocky Mountains, has concurred in proving that this 

 primordial fossiliferous group is not extended downward as claimed 

 by M. Barrande, but that it rests discordantly either on Plutonic 

 rocks or on ancient metamorphic schists in which hitherto no 

 unequivocal fossil forms have been discovered. As this Potsdam 

 group throughout most of its outcrop is confined to a thickness of 

 a few hundred feet, and even where most expanded does not ex- 

 ceed two or three thousand, there appears to be no reason for 

 considering the primordial series as extending farther below the 

 Potsdam sandstone proper than the same restricted limits. 



Adopting the Taconic theory as formerly maintained by Prof. 

 Emmons, the Potsdam group would be included, from the oldest 

 system of fossiliferous rocks, and the latter would have to be 

 sought in the rocky masses on which the Potsdam is seen to have 

 been discordantly deposited. This severance of the Potsdam 

 group from these subjacent rocks is, however, not the view sug- 

 gested by M. Barrande, and maintained by Mr. Marcou in his 

 recent communications to the Society. On the contrary, they pro- 

 pose to leap over the great stratigraphical break which separates 

 them, and to unite the Potsdam group with these older supposed 

 fossiliferous rocks into a single system, the American equivalent 

 of the primordial series of Europe. 



Were we assured of the occurrence of a Primordial fauna in 

 these discordantly subjacent rocks, we might with reason claim to 

 unite them with the Potsdam into a single paleozoic system as 

 here proposed. But until this downward extension of the primor- 

 dial fossils has been unequivocally proved, the universality of the 



