ti86 THE GEOLOGY OP MINNESOTA. 



[Diabase. Taconyte. 



No. 1305. DIABASE. (Dense.} 



Gunflint lake, north shore. 



Ref. Annual Report, xvi, pages 72, 120. 



Meg. Associated with the rock which bears the rusty film seen on some of the 

 rocks of the Animikie. Dark, h'ne, apparently embracing lumps of gray flinty 

 taconyte, like No. 1307. 



Mic. Microliths of feldspar, aiiyitr and of magnetite, very much as in the rock 

 No. 1280, lie in a dim, slightly polarizing brown matrix which may have been at first 

 of glass, but is now composed wholly of the above minerals. The little feldspars are 

 frequently in couples, as if albite twins, but their extremities are not uniformly 

 placed, one or the other projecting too far at one or at both ends. They are also 

 sometimes separated by a portion of the surrounding semi-opaque matter, which is 

 in general heavily charged with the magnetite rods. One section. 



Age. Animikie. 



Hi-nHirL-. This was apparently a surface extension of a basic igneous rock, 

 involving the bottom beds of the Animikie. Its petrographic alliance with No. 1280, 

 which is in the midst of the Keewatin schists, indicates that No. 1280 is really of the 

 date of the sills of the Animikie. The banded structure presented by this slide is due 

 to the concentration of the magnetite in some belts, compared with its scarcity in 

 others. N. H. \v. 



No. 1306. DIABASE. (Dense and magnetited.} 



Same place and same rock mass, but from a specimen numbered 1305 and 1306, showing a gray rilua. 

 Ref. Annual Report, xvi, pages 72, 120 ; Bulletin vi, pages 121, 129, 422. 



Heavy with magnetite. 



Mic. In the midst of the opaque part of this slide are scattered minute light 

 spicules, which can be nothing but feldspars, the same as those seen in No. 1305. 

 The rest of the slide is gray and sub-transparent apparently, a glassy part, less 

 ferruginous, and in this also can be seen the same feldspar microliths. One section. 



Age. Animikie. N. H. w. 



No. 130". TACONYTE. ( si<icriti<: ) 



Same place. 



Ref. Annual Report, xvi, pages 72, 120; Bulletin vi, pages 121, 129. 422. 



May. So-called limestone, of (-Juntiint lake. 



Mi<: The most of this slide is made up of siilrritr ami i/naiiz, the latter being 

 of secondary origin, as shown by its interlocking borders. These are mingled 

 throughout the slide rather uniformly, the siderite grains making roundish patches 

 such as to suggest that it is the result of replacement of some earlier mineral which 

 was granular. 



