PETROGRAPHIC GEOLOGY AND DESCRIPTIONS. 689 



Siderite. Diabase. Quartzyte.] 



No. 1311. SIDERITE (with tuff ). 



North shore of Gunflint lake. 



Bef. Annual Report, xvi, pages 73, 121. 



Meg. Another stage of this rusting rock. (Compare No. 1289). 



Mic. Mainly carbonate of iron, with some scattered dark patches, but not 

 showing any new or even characteristic features, except the prevalence of granular 

 crystals of siderite. The dark patches are presumed to be of rhyolitic origin, one 

 being apparently of glass hardly devitrified. One section. 



Age. Animikie. N. H. w. 



No. 1312. DIABASE. 



At the narrows at the outlet of Gunflint lake. 



Ref. Annual Report, xvi, page 121 ; Annual Report, xvii, pages 199, 204. 



Meg. Black, heavy and close-jointed. 



Mic. The diabasic structure is distinct, notwithstanding the fineness of grain, 

 yet the shapes and the occasional breaking of the feldspar borders by augite show that 

 the two minerals were nearly cotemporary in origin. Many conspicuous magnetite 

 spicules pierce the other minerals, but less frequently the feldspars. The substance 

 lying in the interstices of the feldspars and augites is greenish, sub-crystalline or 

 micro-crystalline, and indistinct, and represents doubtless a devitrified portion of 

 the glassy magma. One section. 



Age. Sill in the Animikie. N. H. w. 



No. 1313. QUARTZYTE. ( Ferriferous.} 



Near the narrows at the outlet of Gunflint lake, on the west side. 

 Ref. Annual Report, xvi, pages 73, 121. 



Meg. Gray, siliceous and magnetited. 



. Mic. Mostly interlocking, secondary quartz, but with considerable iron ore, and 

 a little of rusty fibrous actinolite( ?) Another section having this number is quite 

 different, consisting of very fine t>r flinty texture, and uniform grain; it is like the 

 supposed nodule of glass in No. 1311, and probably was not correctly numbered. Two 

 sections. 



Age. Animikie. 



Remark. The iron ore in this slide consists of both magnetite and siderite, and 

 they present a structure that appears to be a remnant of an earlier taconitic origin. 

 These ores are independent of each other. There is no sign that one was derived 

 from the other, but they appear to have been about cotemporary in origin. The 

 siderite is somewhat limonated, but that is due to recent- exposure. N. H. w. 



No. 1314. DIABASE. (Porphyritic.J 



Animikie bay, west end of Gunflint lake ; also cut by the new railroad. 

 Ref. Annual Report, xvi, pages 78, 85, 121. 



45 



