PETROGRAPHIC GEOLOGY AND DESCRIPTIONS. 363 



Gneiss. Granite.] 



striking feature of the section is the presence of long needle-like crystals of hornblende. 

 The terminal planes are not developed, but cross sections show in good development 

 the prism and brachypinacoid. These hornblendes are quite pleochroic, a being 

 light brownish or straw colored, b greenish brown, and c bottle green. They run at 

 random through the section and at times enclose grains of the other minerals. 



One section. 



Age. Archean' (Keewa tin), u. s. o. 



No. 433. GNEISS. 



Pike river, above the crossing of the old Vermilion road; perhaps in sec. 26, T. 61-16 W. 

 Ref. Annual Report, ix, page 106. 



Meg. Reddish, fine-grained, apparently an alteration from quartzyte or 

 graywacke. 



Mic. Presents an aggregate of much altered feldspar and quartz. The feldspar 

 is crowded with brightly polarizing scales, apparently of Muscovite, and cannot be 

 specifically determined. Some hornblende and a little zircon ( ?) also appear in the 

 slide. A fine sprinkling of dark substances, perhaps of hematite, gives some color to 

 the section in high powers. One section. 



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



No. 434. GRANITE (with IwrnUende). 



Portage between Pike and Embarras rivers, about a mile from the north end of the portage; perhaps in 

 sec. 31, T. 60-15 W. 



Ref. Annual Report, ix, page 106. 



Meg. A medium-grained, gray granite, composed of white to pinkish feldspar, 

 quartz and hornblende. 



Mic. The section is composed mostly of feldspar and quartz. The feldspar is 

 often much clouded by alteration and sometimes indications of a zonal structure are 

 seen. Some of it shows no twinning, but much has very minute twinning lamellae, 

 and a few grains show the microcline grating. No satisfactory determinations were 

 made, but it seems that the feldspar is orthoclase, microcline and anorthoclase or 

 oligoclase. A few areas of chlorite, biotite and epidote are seen; these evidently are 

 the product of alteration of some dark mineral (the hand specimen seems to indicate 

 hornblende). A little apatite and iron ore are also present. 



One section. 



Age. Archean. u. s. G. 



No. 435. GRANITE (with hornblende). 



Embarras river: perhaps S. W. % sec. 7, T. 59-15 W. 

 Ref. Annual Report, ix, page 107. 



Meg. Dark, hornblendic, with reddish feldspar. 



