PETROGRAPHIC GEOLOGY AND DESCRIPTIONS. 587 



Hematite. Amphibolyte. Granite.] 

 Mica schist. 



grown with quartz to form micropegmatyte. The feldspar is in some cases twinned 

 according to the albite law. Its species was not determined. 



Two sections. 



Age. Dike in the Upper Keewatin rocks. u. s. G. 



No. 876. HEMATITE. 



Tower mine, Soudan. 



Ref. Annual Report, xv, pages 251, 387. 



Meg. Steel black, hard, massive hematite; the ore of the Tower mine. 

 No section. 



Age. Lower Keewatin. u. s. G. 



No. 877. AMPHIBOLYTE. 



From a green dike on Menan island in Vermilion lake, near the centre of sec. 36, T. 63-17. 

 Ref. Annual Report, xv, pages 289, 290, 387. 



Meg. The rock has a fibrous schistosity and an irregular distribution of the dark 

 elements, giving it a spotted appearance. 



Mic. It is an amphibolic rock, much resembling the rock from the dyke in 

 Stuntz island, already examined (No. 872), but the amphibole has distinct dichroism, 

 being green when parallel and yellow when perpendicular to the lower nicol or 

 vertical thread of the eye-piece. Zoisite is here found in the same finely divided 

 particles. 



One section. 



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



No. 878. GRANITE. 



From a dike on Menan island, Vermilion lake; sec. 36, T. 63-17 W. 

 Ref. Annual Report, xv, pages 289, 290, 387. 



Meg. A rather fine-grained, pinkish granite, composed of feldspar, quartz and 

 a little biotite. 



Mic. The rock is a granite composed essentially of quartz and feldspar. The 

 size of the component grains varies considerably. The feldspar is mostly untwinned 

 and apparently is orthoclase. Greenish biotite (?), chlorite, epidote and magnetite 

 occur in small amounts. Three sections. 



Age. Dike in Archean rocks. u. s. G. 



No. 879. MICA SCHIST. 



West side of Outlet bay, Vermilion lake; one-fourth mile north of the south side of sec. 14, T. 63-17 W. 

 Ref. Annual Report, xv, pages 293, 388. 



Meg. A medium-grained, hard, rather massive, biotite schist. 

 Mic. The rock is composed of grains, of rather uniform size, of quartz, feldspar 

 and biotite. The feldspar is highly altered and in its alteration has developed 



