536 THE GEOLOGY OP MINNESOTA. 



[Gabl-o. yuartzyte. 



and griinerite. In one of the larger veinlets there are three bands, the inner one 

 being composed of magnetite largely and the outer ones of the two other minerals. 



One section examined. 



Aye. Keewatin. u. s. G. 



No. 767. GABBUO. 



South shore of Gabeinichigaina lake; perhaps in sec. 1, T. G4 (i W. 

 Ref. Annual Report, x, page 98; Annual Report, xv, page 371. 



Met/, A fine-grained, yellowish-gray, crystalline rock, part of the so-called 

 " muscovado." 



Mir. The section is composed of/<"/'/.^'r, //ym/r//r> and hornblende, with a little 

 magnetite, i>yrite and Iriolitc. The feldspar is in elongated crystals, which usually 

 show albite twinning, and also in irregular grains varying much in size and quite 

 commonly showing no twinning. There are, however, all gradations between the 

 two forms of feldspars, and they appear to be of practically the same species. In 

 parts of the section the elongated feldspars are numerous and give a decidedly 

 diabasic texture to the rock. At times the outlines of the feldspars are very irregular 

 or serrate. The feldspar, as well as the pyroxene and hornblende, frequently con- 

 tains numerous small cavities and dark dust-like inclusions. The grains which show 

 albite twinning have extinction angles running up to 34, indicating l<il'<ul<-ite. 



The pyroxene is in small rounded grains and in larger plates which are very 

 irregular in outline, often having a lobe-like border, and include poikilitically small 

 grains of feldspar. The pyroxene when in the plates is usually fissured, and the 

 section has in places a decidedly "granular" aspect. Some of the pyroxene shows 

 a weak pleochroism and an orthorhombic character, though much of it is monoclinic. 

 A few grains show fine polysynthetic twinnings or possibly intergrowths of ortho- 

 rhombic and monoclinic pyroxene. 



The hornblende occurs in the same manner as pyroxene and seems to have been 

 derived from that mineral. 



One section examined. 



Age. Probably Cabotian. u. s. G. 



No. 768. QUAKTZYTE (ivith 



South side of Gabemichigama lake; probably near east line of sec. 1, T. 64 6 W. 

 Ref. Annual Report, x, page 98; Annual Report, xv, page 379. 



Mr;/. A rock, which varies considerably in grain, composed of quartz, pyroxene 

 and magnetite. 



Mic. The section is composed essentially of ]ii/perstlu'in\ i/ixnlz, and i//a</ii(1if<>; 

 the last mineral is in comparatively small amount. The quartz is in grains of more 

 or less rounded outline included in the hypersthene, which is commonly in large 



