242 THE PENOKEE IRON-BE A.EING SERIES. 



<>6. Jaispery and clierty siderite, tVoiii an upper middle horizon. Specimens 12K83 

 (slide 5405), 126S4 (slide 5406), 12685 (slide 5407). All IVoni 1260 N., 1350 W., Sec. 17, 

 T. 47 N., R. 44 W., Michigan. 



This is a laminated rock, composed of an aphanitic to dark gray earthy looking 

 material, which is minutely banded in itself with ligliter and darker shades, and 

 alternates with bands of very bright red jasi)er, which range from the thickness of a 

 sheet of paper to an inch in width. Sp. gr. of 12685, 2.!)k 



The Ja.spcry l)ands in thin section 5405 are seen to be mainly composed of a 

 uniform intermixture of minutely crystalline quartz and bright red hematite, with 

 which arc mingled some magnetite particles. Occasionally the hematite shows 

 rhomliic outlines, but these arc not generally perceptible, perhaps because of the close 

 aggregation of the particles. The dark colored seams prove in the thin section to be 

 in i)art a mixture of crystals of magnetite and minutely crystalline quartz. Such bands 

 as this are found to be directly interlaminated with the bright red jasper. In other 

 cases the darker coloreil bauds owe their dark color to a mixture of minute particles, 

 which are in part probably of a carbonaceous nature. Such bands as this are found 

 interlaminated more directly with those ])ortions in which carbonate of iron is abun 

 dant (5407). The lighter colored portions of 5407 are in part a mixture of iron 

 carbonate, brown and red iron oxides, magnetite particles, actinolite needles, and 

 minutely crystalline silica, the latter mineral being the least plentiful. Still other 

 bands arc made up mainly of a silica which ranges fiom very nunutely crystalline to 

 nearly o- (piite amorphous. In this tlint ov <'hcrt arc found remains of bands of iron 

 carbonate, single rliomboliedra of the same, and scattering crystals of magnetite. 



67. Actinolitic magnetite-slate, from a high horizon. Specimens 12703 (slide 

 5420), from 1180 X., ('>:):, W.; 12704 (slide 5421); from 1200 X., 655 W., Sec. 17, T. 47 

 X., R. 44 W., ^lichigan. 



A very heavy aphauitic slaty rock, made up of minute alternating laminte of 

 dark gray and black shades. Portions of the specimens show a distinct metallic 

 luster, particularly on the black lamina', and quite large ])ieces are lifted by the mag- 

 net. Interlaminated with this material are bands of a nuu'h lighter color. 



In thin section, the lighter colored bands (5420), last referred to, are seen to have 

 a minutely crystalline siliceous groundmass, in whieh are included numerous minute 

 actinolite needles and particles of iron oxide, including the tnagnetic oxide. The 

 actinolite is on the whole (piitc as plentiful as the silica, and in portions of the section 

 is aggregated into felted masses. The earthy black portions of the rock present a 

 section which dilfers liom that Just described m:iinl.\- in the relatively great abundance 

 of iron oxides, jiarticularly m;ignetitc; this last mincial being more especially aggre- 

 gated into irregular lamimc. Actinolite is very abundant, constituting in considerable 

 portions of the section an inm-stained felted mass of minute needles. 



