ROCKS ON LAKE SUPERIOR. 



93 



In his hypothetical section, however (p. 187), the higher and lower members 

 of the assemblage are treated as conformable with each other. 



Before proceeding to quote the language accompanying Sir William 

 Logan's formal announcement of the adoption of the terms " Laurentian " 

 and " Huronian," in the sense now understood, it will help to a compre- 

 hension of his positions to state, in appropriate citations, what had been 

 learned about rocks, assumed to be of Huronian age, about the shores of 

 Lake Superior. 



Citations from the Founders touching the Vicinity of Lake 



Superior. 



Logan's first Report. — In his report of progress for 1846-'47, Director 

 Logan described the rocks on the north shore of Lake Superior as consisting 

 of the following divisions : 



5. Sandstones, limestones, indurated marls and conglomerates, interstrati- 

 fied with trap, 



4. Bluish slates and shales, interstratified with trap. 



Unconformity. 



3. Chloritic and partially talcose and conglomeratic slates. 



2. Gneiss. 



1. Granite and syenite. 



The following is a portion of Director Logan's remarks on these rocks : 



" The gneiss is succeeded by [3] slates of a general exterior dark green color, often 

 dark gray in fresh fractures, which at the base appear occasionally to be interstratified 

 with beds of a feldspathic quality of the reddish color belonging to the subjacent granite 

 and gneiss, -s^- * -5«- Some of the beds havH the quality of a greenstone ; others that 

 of a mica slate, and a few present the character of quartz rocks. Rising in the series, 

 these become interstratified with [3] beds of a slaty character, holding a sufiScient 

 number of pebbles of various kinds to constitute conglomerates. The pebbles seem 

 to be of various qualities, but apparently all derived from hypogene rocks. -5^ * * 

 The formations which succeed [4] rest unconformably upon those already mentioned. 

 The base of the lower one where seen [in Thunder bay] in contact with the subjacent 

 green slates [3] presents conglomerate beds, probably of no great thickness, composed 

 of quartz pebbles chiefly, with a few of red jasper, and some of slate in a green arena- 

 ceous matrix, consisting of the same materials in a finer condition (pp. 8-17). * * * 

 The chloritic slates at the summit of the older rocks, on which the volcanic formations 

 rest unconformabl}^, bear a strong resemblance to those met with in the upper part of 

 Lake Temiscaming, on the Ottawa, and it appears probable they will be found iden- 

 tical " (p. 34).^ 



Murray's Account of the same Region. — Mr. Murray, in the report for the 

 same year (1846-47), has an independent account of the formations in the 



*See also Logan, Report for 1848. p. 29. 

 XV— Bull. Geol. Soc. Am., Vol. 2, 1890. 



