356 THE GEOLOGY OF MINNESOTA. 



[Granite. Schist. 



No. 411. GRANITE. 



Same locality as No. 409. 



Ref. Annual Report, ix, page 100. 



Meg, Medium-grained, pinkish granite, composed of a flesh-colored feldspar 

 and quartz. There are also a few darker areas now mostly occupied by iron oxide 

 from the decay of some dark mineral. 



Mic. The section shows a granitic aggregate of quartz and feldspar. The 

 feldspar is much clouded. A considerable part of it shows microcline grating, while 

 much is finely twinned by the albite law. The twinning lamellae are often discontin- 

 uous and bent, and there is a fine-grained aggregate between some of the grains, the 

 whole suggesting that the rock has been subjected to pressure.. These effects, 

 however, cannot be carefully studied owing to the extreme thickness of the section. 

 There are brownish stains throughout the section, and a few small, opaque, black 

 areas, on the borders of which can sometimes be seen a very little chlorite. One of 

 these areas is made up partly of biotite. 



One section. 



Age. Archean (igneous). u. s. G. 



No. 412. BIOTITE SCHIST. 



Same locality as No. 409. 



Ref. Annual Report, ix, page 100. 



Meg. A roughly schistose, gray rock, rather fine grained. It is composed of 

 biotite, sometimes in scales of considerable size, and a granular aggregate of 

 apparently quartz and feldspar. 



Mic. The section is quite thick. It shows much feldspar, a considerable part 

 of which is much clouded, usually not twinned. Two grains, each of which gave a 

 positive bisectrix, had extinction angles of 4 and 6. This result would place the 

 the feldspar near oligoclase or orthoclase. Biotite and chlorite are both present in 

 considerable amount, and quartz is not uncommon, although not nearly as abundant 

 as the feldspar. 



One section. 



Aye. Archean (Coutchiching). u. s. G. 



Remark. At the place where were obtained Nos. 409-412 there is an exposure 

 of gneiss which passes confusedly to granite and to mica schist, but has no general 

 schistose structure. There are small patches of mica schist surrounded by granite 

 and bands of coarse granite running through the whole, varying to a fine granite. 



N. H. w. 

 No. 413. BIOTITE SCHIST. 



From the Vermilion rapids, at the outlet of Vermilion lake northward ; N. E. j N. W. % sec. 11, T. 63-17 W. 

 Ref. Annual Report, ix, page 100. 



