PETROGRAPHIC GEOLOGY AND DESCRIPTIONS. 831 



Sideryte. Actinolyte.] 



No. 2052. SIDERYTE. 



From the prominent hill near the centre of sec. 24, T. 65-4 W.; west of Gunflint lake. 

 Ref. Annual Report, xxiv, page 27. 



Meg. A medium-grained, gray rock, in places showing fine bandings; effervesces 

 freely in cold hydrochloric acid; weathers rusty. Is apparently composed of siderite, 

 calcite and actinolite, the first in large amount and the last in fine star-like rosettes. 

 Compare Nos. 437 and 1289. 



Mic. A thin section made by Dr. Otto Kuntze shows this rock consists appar- 

 ently only of siderite and actinolite (or cummingtonite). In the former are many 

 globular grains of siderite, a feature that has been seen to characterize several of 

 the secondary minerals generated by metamorphism. The latter mineral is prevail- 

 ingly in sheaves that spread at each end, but sometimes from one end a ramifying 

 lot of fibres extend further and make connection with similar extension from some 

 other sheaf. The rock is like No. 1289, and is allied to No. 437, and both are from 

 the iron-bearing membe'r of the Animikie. Magnetite dust is thick in spots, rendering 

 some of the siderite nearly opaque. 



Age. Animikie (iron-bearing member). N. H. w. 



No. 2053. ACTINOLYTE. (Rock: zirkelyte.) 



N. W. M S. E. % sec. 24, T. 65- 4 W.; west of Gunflint lake. 

 Re.f. Annual Report, xxiv, page 27. 



Meg. The rock is full of spherical masses which vary from one-eighth to one- 

 half inch in diameter. They are very distinct on weathered surfaces, but on fresh 

 fractures are hardly discernible. The spherical masses resist the effects of weathering 

 much better than the interstitial material. The whole rock is quite fine grained and 

 is greenish-gray in color, the spherical masses being a little darker colored than the 

 rest of the rock. There is some carbonate present, probably calcite, as the rock 

 effervesces a little in cold hydrochloric acid, and probably also siderite, as the rock on 

 weathering turns yellowish with iron oxide. This rock is developed in the Animikie 

 in connection with a horizontal fault plane or slip in which is a coarse breccia. 



Mic, In ordinary light the spherical masses in the slide are quite distinct, and 

 sometimes they are partially outlined by an area which contains considerable yellow 

 iron oxide. The interstitial material, which is not abundant, is lighter colored than 

 the spherical masses, and seems to have lost considerable in the grinding of the slide. 

 Under crossed nicols the spherical masses are not very distinct, and the whole section 

 breaks up into a closely matted mass of minute amphibole fibres, which appear to 

 be grunerite-cummingtonite. One section. 



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



Iteinark. In some parts this rock is finely scoriaceous; indeed, the interstitial 

 areas between the spherical masses are uniformly porous. The balls that present 



