PETROGRAPHIC GEOLOGY AND DESCRIPTIONS. 889 



Granite. Graywacke.] 



Mic. The section shows boih rocks. The syenyte is composed essentially of 

 (1) An almost opaque feldspar, which, notwithstanding its alteration, shows traces 

 of polysynthetic twinning; (2) A fresh feldspar with abundant twinning lamella?; 

 and (3) A few pieces of green hornblende. The small part of the amphibolyte in 

 the section is seen to be made up almost entirely of green, highly pleochroic horn- 

 blende; a small amount of altered feldspar is also present. One section. 



Age. Archeau. u. s. G. 



No. 368G. GRANITE. 



Kawishiwi river (west shore) in S. W. % sec. 34, T. 63-10 W. 

 Ref. Annual Report, xx, pages 43, 98. 



Meg. A medium-grained, brownish granite forming the shore of the river. 



Mir. The entire section shows essentially a granitic aggregate of orthoclase, 

 hornblende and quartz. The orthoclase is gray and usually shows a cloudiness due 

 to alteration; a few of the grains show a polysynthetic twinning lamellae. The 

 hornblende is the ordinary green, highly pleochroic variety, and is completely allot- 

 riomorphic; it has altered in some places to chlorite, but elsewhere appears to be 

 quite fresh. Quartz is scattered through the whole section, but is not noticeable 

 macroscopically; it presents the characters of ordinary granitic quartz. It occurs 

 oftentimes in polysomatic areas, and a large number of the grains show decided 

 undulatory extinction. The quartz makes up less than ten per cent of the whole 

 rock. Apatite, sphene and magnetite are the accessory minerals; they all occur in 

 only small amount. The apatite is in both short, stout and long, slender prisms. 

 The sphene and magnetite show no characteristic crystal outlines. One section. 



Age. Archean. u. s. G. 



No. 383G. GRAYWACKE. (Fine.) 



North branch of the Kawishiwi river, N. E. J N. E. y sec. 28, T. 63-10. 

 Ref. Annual Report, xx, pages 46, 99. 



Meg. Fine graywacke, evidently somewhat hardened by metarnorphism. In 

 the field shows distinct stratification. 



Mif. The rock shows a slight schistosity, the graining being elongated prevail- 

 ingly in one direction, and the darker elements arranged in broken lines or shreds 

 in the same direction. 



The most noticeable feature is the decayed condition of the feldspathic grains. 

 They are permeated with Muscovite, chlorite and epidote, which, in finer grains, render 

 the original feldspar so vague and invisible that generally no part of it is sufficiently 

 intact to afford any characteristic tests for species. Some of them can be seen to 

 have been twinned formerly on the albite plan. These decayed grains do not show 

 any conspicuous, and but rarely a narrow, indistinct, broken, reconstructed margin. 



