OP ARTS AND SCIENCES. 191 



scarcely differing from the one in the Calciferous.* So much for the 

 St. Lawrence region. 



" But now as to Iowa and the "West, I understand Owen to say, 

 that far below what he would call the Potsdam proper, there are beds 

 with Primordial fossils (he does not use the word, but we may). Here, 

 then, we have got down to another series, which no doubt appears to 

 be conformable with the Silurian, but with peculiar fossils and in 

 abundance. These no doubt should be regarded as the ujiper part of 

 the Primordial series, and it may be contain sandstones. I have not 

 Owen's book to refer to. Again, not having seen these beds, I have 

 no satisfactory knowledge how they lie ; but those sandstones may be 

 placed as you suggest. And I go further, and say, if you believe you 

 can make out a good case vrith the Potsdam anywhere, I never shall 

 object, for I have no wants except truth. 



" But the break, or the heavy conglomerate at the base of the Pots- 

 dam in St. Lawrence County, seems to me to favor the position I 

 took, that the sandstone and conglomerate beds are at the base of the 

 Silurian. I merely suggest these fl^cts for your consideration. 



" In conclusion, allow me once more to thank you for all you have 

 done in American geology, and especially for the benefit you have 

 been to your servant, 



" E. Emmons." 



This letter is the last I received from Emmons. After the break- 

 ing out of the civil war, I was unable to send either the memoir of 

 Barrande, " Documents anciens et nouveaux sur la Faune Primordiale 

 et le Systeme Taconique en Amerique," or my observations and 

 pamphlets of 1861 and 1862, entitled, "The Taconic and Lower Si- 

 lurian Rocks of Vermont and Canada " (Proceedings Bost. Soc. Nat. 

 Hist., Nov. 6, 1861), and "Letter to M. .Joachim Barrande on the 

 Taconic Rocks of Vermont and Canada" (Cambridge, 1862). The 

 impossibility of reaching him left Dr. Emmons partly in ignorance of 

 the efforts made in favor of his "Taconic system." 



These last letters, the two dated in January, 1861, are given to 

 show his opinions at the moment of the change made in the official 

 classification of the geological survey of Canada. They were written 

 in ignorance of the printed letter of Logan to Barrande, and it is 

 doubtful if Dr. Emmons ever saw it. 



* Several fossils have been found since in the Potsdam sandstone near Keese- 

 ville, besides the Lingula (Oholella) prima, such as Linrjulrpsis minima, Conocepha- 

 lites minutus and C. Verrucosus Whitf, entirely Primordial fossils. 



