PETROGRAPHIC GEOLOGY AND DESCRIPTIONS. 313 



Granite.] 



Prof. C. F. Sidener, who analyzed this rock, obtained the following result (Bulletin vi, page 121): 



Silica, 2.70 per cent. 



Alumina, .35 



Ferric oxide, 17.23 



Ferrous oxide, - 8.35 



Calcium carbonate, 49.80 



Magnesium carbonate, 19.65 



Potassium oxide, .04 



Sodium oxide, .20 



Water, .47 



Total, 98.79 per cent. 



Aye. Taconic, near the base of the Animikie, or perhaps Upper Keewatin. 



Remark. The stratigraphic horizon of this limestone is much below that of the 

 calcareous conglomerate of Grand Portage island (No. 254) and of the nondescript 

 somewhat vesicular calcareous rock (No. 255) which overlies it. Further examina- 

 tion has shown that the latter was cotemporary with a volcanic epoch in the 

 Keweenawan near the bottom of the same, while the former is near the base of the 

 Animikie, or belongs in the Keewatin. N. H. w. 



No. 313. GRANITE. 



N. E. % sec. 24, T. 65-4 W., south shore of Magnetic lake (a part of Gunflint lake north of the narrows). 

 Ref. Annual Report, ix, page 83. 



Meg. A light-colored, micaceous, medium-grained rock. 



Mic. With much quartz is mingled microcline and perhaps orthodase, biotite 

 and chlorite. Some of the feldspar is finely twinned on the albite plan and probably 

 comes near oligodase. 



One section. 



Age. Archean (igneous). N. H. w. 



No. 314. GRANITE (with hornblende). 



North shore of Magnetic lake; S. E. ^ sec. 13, T. 65-4 W. 



Ref. Annual Report, ix, page 83. Compare No. 650 (W.), Annual Report, xvi, page 237. 



Meg. A rather coarse pinkish granite, composed of quartz, pink feldspar usually 

 not showing twinning strias, and hornblende. There is some epidote present, and also 

 probably c/ilorite and biotite. A noticeable feature of the rock is the presence of 

 several good sized crystals of a cinnamon brown mineral, most probably sphene. 



No section. 



Age. Archean (igneous). u. s. G. 



No. 315. GRANITE (with Jiomblende). 



First falls north of Gunflint lake, on the international boundary; N. E. % N. E. % sec. 1.3, T. 65-4 W. 

 Compare Nos. 800, 1318; also, No. 649 (W), Annual Report, xvi, page 233, and No. 62 (G), Annual Report, xvii, 

 page 160. 



Ref. Annual Report, ix, page 83; Annual Report, x, page 106. 



