634 THE GEOLOGY OF MINNESOTA. 



[Iron Ore. Quartz-porphyry. Amphibolyte. 



Mic. The cementing background is a long fibrous mineral, having a low double 

 refraction and parallel extinction. Its highest color rotated between nicols is 

 bluish gray in the first order. There is not enough of this mineral visible 

 in the section to allow of its specific determination. The magnetite, which, on 

 analysis, gave a trace of titanium, is in form of a fine powder, distributed through 

 this matrix. One poor section. 



Age. Archean (Lower Keewatin). N. n. w. 



No. 1025. IRON ORE. (Magnetic.) 



Near the same locality as the last. 

 Kef. Annual Report, xv, pages 328, 394. 



Meg. Similar to the last, but not schistose; also lacking the bluish color of 

 the last. 



Mic. About one-half of this rock is of magnetite, the rest being apparently the 

 same fibrous mineral as seen in the last, but here showing more favorably and 

 having a colored double refraction, which, with other characters, denotes adinolite. 

 One section. 



Age. Archean (Lower Keewatin). N. H. w. 



NO. 1025A. QUARTZ-PORPHYRY. 



Apparently overlying the last. 

 Kef. Annual Report, xv, page 394. 



Meg. Coarsely granular, with feldspar and quartz. 



Mic. The large feldspar crystals and the rounded quartz grains lie in the midst 

 of a fine, granular, secondary matrix. The feldspars are clouded with impurities, 

 but show their coarse twinning (albite and pericline). The quartz is broken and 

 also streaked by bands of impurities. The enclosing matrix has some hor/th/cndc* 

 which are large, distinct and idiomorphic, and some that are partly changed to 

 chlorite, much interlocking fine quartz, leucoxene, of which some larger grains are 

 straw-yellow, but the most are white, passing to sub-opaque, a little fine epidote and 

 muscovite and a single grain of apatite. One section. 



Age. Archean (Keewatin). 



Remark. This rock resembles the quartz-porphyry of Kekequabic lake. 



N. H. w. 

 No. 1026. AMPHIBOLYTE. 



Prom the northern island crossed by the section line between sees 11 and 12, T. 64-11. Basswixul lake. 

 Kef. Annual Report, xv, pages 357, 394. 



Meg. A fine-grained, fibrous, green rock. 



Mic. The hornblende, broken by considerable secondary quarts, is mostly in a 

 fibrous condition, but sometimes over the area of a crystal it shows not only its 



