90 THE VERMILION IRON-BEARING DISTRICT. 



quartzite series, and the Sioux quartzite series. Under the Huronian is the 

 Laurentian, separated from it by a great unconformity. This is a series of 

 granites, gneisses, hornblende-schists, mica-schists, and other green schists. 



1889. 



Hall, C. W. The distribution of the granites of the Northwestern States, and 

 their general lithologic characters: Proc. Am. Assoc. Adv. Sci., Thirty-seventh 

 Meeting, 1889, pp. 235-226. 



In the above paper Hall describes the distribution of the granites of 

 the Northwestern States, particularly those of Minnesota. 



In Minnesota they occur (1) in several belts along the Canadian 

 boimdary projecting southwesterly into the State; (2) as quite prominent 

 masses, whether connected with those along the boundary or not, aroiind 

 Vermilion, Snowbank, and other lakes; (3) forming the Mesabi or Giant 

 range; (4) at a number of places in the central part of the State. These 

 are found to be either intrusive or granitic vein-stones, the latter being 

 insignificant in quantity. The granites of Minnesota as to age are probably 

 later than the Laureiitian floor of the continent, but earlier than those of the 

 Agnotozoic era. 



They belong to one of the three or four grand periods of eruptive 

 activity determinable in the Northwestern States. 



WiNCHELL, N. H. Seventeenth Ann. Rept. Geol. and Nat. Hist. Survey Minn., 

 for 1888, 1889, pp. 5-71; see also the Animikie black slates and quartzites, and the 

 Ogishki conglomerate of Minnesota, the equivalent of the "Original Huronian:" 

 Am. Geologist, Vol. I, 1888, pp. 11-14; also Methods of stratigraphy in studying the 

 Huronian: Am. Geologist, Vol. IV, 1889. pp. 313-367. 



In this, Winchell gives a review of the work done upon the crystal- 

 line rocks of northeastern Minnesota by the State survey, showing the 

 progression in the ideas held concerning their characters and stratigraphy 

 (pp. 6-28). Then follows a summary of the results of the investigations 

 as they appear up to that time (pp. 28-74). In many points the conclusions 

 and facts are the same, of course, as in the previous reports. The Lauren- 

 tian age (pp. 28-31) is made to include the gneiss, granitic, and syenitic, but 

 excludes the crystalline schists. It is the fundamental gneiss of Minnesota. 

 "It resulted from the fusion and recrystallization of the earliest sedi- 

 ments" (p. 28). 



