760 THE GEOLOGY OF MINNESOTA. 



[Gabbro. Taconyte. Breccia. 



No. 1687. GABBRO. (S/tcored. ) 



Same place as No. 1684, Philbrook, Morrison county. 

 Ref. Annual Report, xxi, page 155. 



Meg. Schistose. 



M!c. The original crystalline structure is entirely broken up and fragmentary. 

 The augite has given place to hornblende, polychroic (blue, green, yellow) and fibrous; 

 olivine is wanting, and magnetite is abundant. The feldspars, while broken and 

 dislodged, are not saussuritized markedly, although some small grains of zoisite and 

 of sericite are developed. The most frequent element which permeates the broken 

 feldspars is hornblende in form of more minute fibres. Calcite is generally dis- 

 tributed. One section. 



Age. Probably Archean. 



Remark. The marked contrast between this rock, which is known to have been 

 sheared, and No. 1686, which consists largely of zoisite, without other signs of 

 shearing, taken from the same rock mass,* rather indicates that the shearing process 

 is not that which first tends to the destruction of the feldspathic element in this 

 gabbro. The areas occupied by these variations from the normal condition of this 

 gabbro are quite small. N. H. w. 



No. 1688. 'TACONYTE. 



"Three samples of taconyte showing various conditions of change toward hematite, Hale mine, near 

 Merritt, on the Mesabi range." 



Ref. Annual Report, xxi, page 155. 



Meg. One of the samples shows a very hard, fine-grained, grayish taconyte, iron- 

 stained and altered to limonite and hematite along fissures. Another sample is a 

 yellowish chert with considerable limonite, and another is a similar cherty rock with 

 crystallized limonite. No section. 



Age. Animikie (iron-bearing member.). u. s. G. 



No. 1689. BRECCIA (?) 



From the Cincinnati property (sec. 2, T. 58-16 W.), Mesabi Iron range. 

 Ref. Annual Report, xxi, pages 118, 155. 



Meg. A heavy, iron-bearing, black taconitic rock, containing fragments of dark 

 chert and magnetite. The fragments are in part rounded and in part angular and 

 often not sharply separated from the matrix. The rock may be a conglomerate or a 

 breccia, but from its position, apparently near the base of the black slate member of 

 the Animikie, it seems more likely to be a breccia. No section. 



Age. Animikie (near the base of the black slate member). u. s. G. 



Remark. This remarkable rock has not as yet been examined microscopically. 

 It may be of the nature, in part, of a volcanic tuff. N. H. w. 



