PETROGRAPHIC GEOLOGY AND DESCRIPTIONS. 611 



Syenyte. Granite. Gabbro.] 



No. 952. SYENYTE. (Hornblendic. ) 



West side of White Iron lake; sec. 6, T. 62-11 W. 

 Ref. Annual Report, xv, pages 329, 390. 



Meg. A medium-grained, pinkish-gray, hornblende syenyte. 



Mic. The section is composed essentially of feldspar and green, more or less 

 fibrous hornblende. The feldspar is orthoclase and acid plagioclase and perhaps also 

 anorthoclase. Other minerals present in small amount, are: chlorite, magnetite, 

 epidote, sphene and quartz. A microchemical test, with hydrofluosilicic acid, of a 

 grain of feldspar showed the presence of soda and lime, but practically no potash. 



One section. 



Age. Archean. u. s. G. 



No. 953. GRANITE. (Porphyritic.) 



Sec. 19, T. 62-11 W.; river bank on the portage from White Iron lake to Birch river. 

 Ref. Annual Report, xv, pages 329, 334, 336, 390. 



Meg. A medium-grained, pinkish, hornblende granite, with porphyritic crystals 

 of flesh-colored feldspar. 



Mic. The rock is quite similar to No. 952, except for the presence of more 

 quartz and some microcline. A microchemical test, with hydrofluosilicic acid, of 

 one of the porphyritic feldspars gave much soda and potash and almost no lime, thus 

 indicating anorthoclase. A test of a grain of feldspar from the groundmass gave the 

 same result. 



One section. 



Age, Archean. u. s. G. 



No. 954. GABBRO. (Olimnitic.) 



Near the N. W. J sec. 17, T. 61-11 W.; east side of Birch lake. 



Ref. Annual Report, xv, pages 332, 333, 390; Annual Report, xvii, pages 194, 207. 



Meg. A rather coarse-grained, gray gabbro. Feldspar is the most abundant 

 mineral and occurs in grains and plates which frequently show the striation due to 

 polysynthetic twinning. Biotite is quite noticeable, and pyroxene, olivine and 

 magnetite also occur. The mass is in laminae due to the linear arrangement of the 

 olivine grains. 



Mic. The sections show a fresh gabbro. The minerals are feldspar (probably 

 labradorite), olivine, pyroxene (augite and some pleochroic pyroxene which is probably 

 hypersthene), biotite, magnetite, py rite and greenish and brownish alteration products 

 of the olivine. The rock exhibits many interesting features and would make a good 

 subject for detailed study. 



Three sections. 



Age. Cabotian. u. s. G. 



