682 THE GEOLOGY OP MINNESOTA. 



(Gabbro. Dioryte. Taconytn. 



to be considered nearer siderite than calcite; and taken in connection with the rusty 

 film that coats all weathered surfaces, there is no escape from calling them siderite. 

 In all parts of the slide, and more abundantly in some than in others, the substance 

 in which these rhombs lie is seen to be isotropic, though transparent, resembling 

 glass. In high power of magnification and with strong light, there appear between 

 crossed nicols dim, minute crystalliths whose forms cannot be made out any further 

 than to determine that usually they show some elongation. They do not polarize in 

 colors, but show only the lowest grays of the first order. One section. 



Age. Bottom layers of the Animikie. N. H. w. 



No. 1292. GABBRO. (Iron-bearing.) 

 Same as No. 1288. 



Meg. With olivine. 



Mic. Brown hornblende in considerable quantity separates the magnetite from 

 the other minerals, whether olivine or plagioclase, and is sometimes surrounded by 

 the magnetite. A little augite is in the slide. One section. 



Age. Cabotian. N. H. w. 



No. 1293. DIORYTE(?) 



North shore of Iron lake. From a boulder. 

 Ref. Annual Report, xvi, pages 78, 120. 



Meg. A dark crystalline rock composed mainly of hornblende and feldspar, with 

 some biotite. The following description is from the Sixteenth Annual Report, page 78: 



"Rock No. 1293 is from a boulder, north shore of Iron lake. The interesting 

 feature in this boulder, which was rounded, and evidently far transported by drift 

 agents, is that it is made up of boulders. Originally the mass measured three feet by 

 two and one-half feet by four feet, and by the action of fire large slabs have been 

 made to drop off. Otherwise no samples could have been obtained with any means 

 which we could control. This is not only made up of boulders, but it is from the 

 mica-hornblende schist or Vermilion group [Coutchiching], and shows that conglom- 

 erates there have been converted into crystalline rock. The small boulders are of 

 greenstone, mica schist and changed greenstone. The matrix is granulyte or 

 granite." No section. 



Age. Archean. u. s. G. 



No. 1294. TACONYTE. 



On the town line (if extended into Canada) between T. 65-1 and T. 65-2 W., about half a mile from Gun- 

 flint lake. 



Ref. Annual Report, xvi, pages 69, 120. 



Meg. Appearing like a conglomerate, or breccia, ferruginous and somewhat 

 crumbling. 



Mic. The section consists of interlocking quartz grains of secondary origin, 

 serving as matrix for rather large, pebbly and concretionary grains, which are stained 



