RESUME OF LITERATUEE. 101 



being' that the gabbi'O flowed back uoithward over older formations and came onto 

 the gneiss [pp. 44-45]. 



Bowlders of characteristic gabbro and red syenite, and of quartz porphyry, occur 

 abundantly in the later "traps" of the Cupriferous [p. 45]. 



WiNCHELL, H. V. Geological age of the Saganaga syenite: Am. Jour. Sci., 3d 

 series, Vol. XLI, 1891, 386-390. 



H. V. Winchell iu 1891 states that the syenite of Saganaga Lake is 

 conglomeratic in places and contains pebbles which are similar to each 

 other, being mostly composed of lamellar augite, with or without grains of 

 feldspar, but there are no pebbles of sedimentary rocks or of syenite or 

 jasper such as occur in the Kewatiu conglomerates. 



In the Saganaga syenite at the end of the portage on Grranite River 

 is a band of silica IJ inches in diameter and 3 feet in length. This is 

 presumed to have been formed by chemical precipitation from heated 

 oceanic waters." 



North of Saganaga Lake the syenite grades into greenish feldspathic 

 and sericitic schists and agglomerates without the usual intervening belt of 

 crystalline Vermilion schists. From these facts it is concluded that the 

 syenite is simply the result of the locally intense metamorphism of 

 Kewatin rocks, and is thus of Kewatin age. 



Finally, as bearing iipon the economic side of the question it is 

 suggested that — 



If the Saganaga sj-enite be of the Keewatin age and contain chalcedonic silica in 

 an original, unchanged condition it is not unlikely to contain also Keewatin iron-ore 

 deposits free from titanium and of high grade in other respects. It can thus no 

 longer be laid down as a law for explorers in the Northwest that the gneisses contain 

 no iron-ore deposits [p. 390]. 



Winchell, N. H. and H. V., The iron ores of Minnesota, Bull. No. 6, Minn. 

 Geol. and Nat. Hist. Survey, 1891, 430 pages, with geological map and section. 



N. H. and H. V. Winchell in 1891 give an extended treatment of the iron 

 ores of northeastern Minnesota and the rocks in which they are contained. 

 Magnetic iron ore is not of great importance. Isolated deposits are reported 

 in the mica-hornblende-schists and in a massive hornblende-mica rock of 



« Winchell, N. H. and H. V., On a possible chemical origin of the iron ores of the Keewatin in 

 Minnesota: Proc. Am. Assoc. Adv. Sci., Thirty-eighth Meeting, 1890, pp. 235-242. Am. Geologist, 

 Vol. IV, 1891, pp. 291-300; 382-386. Also The iron ores of Minn., Geol. Nat. Hist. Survey Minn., 

 1889, Bull. No. 6, 430 pages. 



