192 PROCEEDINGS OF THE AMERICAN ACADEMY 



The letter of Billings, 21 December, shows an acquaintance with 

 the memoir containing extracts from three letters of Barrande ; the 

 official date of this memoir is 24 December, 18 CO, printed at the foot 

 of the page, and its having been sent to Montreal before its issue at 

 Boston, and before I had seen it even, is a sufficient proof of the inter- 

 est excited by it; it was in part reprinted immediately in several 

 scientific journals. 



1861. — Logan could hardly delay any longer his answer to Bar- 

 rande's letter of 1860, containing a copy of the letter to Prof. Bronn. 

 The publication of this letter in English rendered it necessary for him 

 to make a decision. After great hesitation he decided to write a 

 printed letter, entitled, " Remarks on the Fauna of the Quebec Group 

 of Rocks, and the Primordial Zone of Canada, addressed to M. Jo- 

 achim Barrande." 31 December, 1860, is the date of the letter; 

 the date of the impression is 3 January, 1861, and it was distributed 

 and sent from Montreal on the 12th of January. This document of 

 five pages is the letter of a diplomatist rather than of a geologist. 



The explanation of the stratigraphy of Point Levis is unintelli- 

 gible ; so much so, that some months later he was unable to explain it 

 to me on the map made by himself of Point Levis ; and that on the 

 ground, after two successive studies made in 1861-62, I was unable 

 to make this explanation agree with what exists at Point Levis. 



The principal concession of his letter is the existence of what he 

 erroneously calls the "Quebec group" (it is in reality the "Point 

 Levis group"), of a thickness of perhaps some 5,000 or 7,000 feet, 

 which he regards as equivalent to, and on the horizon of, the two divis- 

 ions of Chazy limestone and Calciferous sandrock with points of "over- 

 turned Trenton " from time to time framed therein, in Vermont, but 

 not in Canada. Further, he thinks the " Olenus shales of Georgia " 

 are interposed in the strata of the Quebec group, and that the whole 

 rests upon the " Potsdam formation," which, according to him, forms 

 the " New Primordial zone in Canada." A paragraph is given to 

 Lake Superior, where he looks upon the sandstone as Chazy, Calcifer- 

 ous, and Potsdam, or the equivalent of his Quebec group ; and the 

 rocks containing copper as belonging to his Huronian system. 



Finally, he admits that Prof. Emmons was certainly right to main- 

 tain that the rocks in Vermont are older than the Birdseye forma- 

 tion ; and that Billings regards the trilobites of the Quebec group as 

 indicating that this group is nearly at the base of the second fauna. 

 The last phrase declares Georgia to be a constituent part of the Pri- 

 mordial zone, contrary to what he had said a few paragraphs back. 



