352 THE GEOLOGY OP MINNESOTA. 



[Quartz. Schist. Granite. 



the presence of large amounts of calcite, or more probably both calcite and siderite, 

 as some of this material shows a very slight absorption. 



One section. 



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



No. 400. QUARTZ. (Vein.) 



Same locality as No. 399. 



Ref. Annual Report, ix, page 98; Annual Report, xviil, pages 20, 21; Annual Report, xix, pages 125, 127. 



Meg. Specimen missing (used in assay). 



Mic. The section shows coarsely crystallized quartz which has been fissured and 

 in places evidently crushed into a mass of finer grains. The quartz shows very pro- 

 nounced undulatory extinction and is cloudy, the cloudiness being due to the presence 

 of numerous minute dust-like particles and cavities containing liquid; occasionally a 

 cavity with a bubble is seen. Besides the quartz there are present small amounts of a 

 gray opaque substance, reddish and yellowish stains, chlorite, pi/rite and a metallic 

 glistening mineral, perhaps chalcocite. 



One section. 



Age. Vein in Archean (Keewatin) rocks. 



Remark. See chemical analysis under No. 395. u. s. G. 



No. 401. HORNBLENDE SCHIST. 



Vermilion lake; probably from Menan island, or a little island just to the east of it; S. E. J^ sec. 36, 

 T. 63-17 W. 



Ref. Annual Report, ix, pages 98, 99. 



Meg. A gray, compact, fine-grained schist, with a distinct fibrous elongation. 

 The rock is arranged in laminations that run S. 55 W., sloping south and embraces 

 laminations and wide belts, also conformable with the rest (except where large areas 

 come in) of No. 402. 



Mic. The colored, shining mineral which gives the rock a micaceous aspect, 

 proves not to be of mica, but of hornblende with a little chlorite, probably of the 

 species pennine. The rock also contains feldspar, but much decayed, and much 

 quartz, the latter probably of secondary date. Some biotite, and also epidote, the 

 latter in large grains, appear in the slide, with some altered garnet, the alteration 

 product being chlorite. There is also a little sphene, and of ilmeiiitc, having a border 

 of leucoxene. There are a few crystals of apatite and others of zoisite. 



Two sections. 



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



No. 402. GRANITE. 



Same place as No. 401. 



Ref. Annual Report, ix, pages 98, 99. 



Meg. Light colored, slightly chloritic granite. 



