PETROGRAPHIC GEOLOGY AND DESCRIPTIONS. 295 



Quartzyte. Barite, calcite.] 



Graphite, which resembles magnetite, even in reflected light, is common. It is 

 an element of the sedimentary strata. 



Penninile, having nearly the same appearance as in No. 265, but in less amount, 

 seems to exhibit a gradation in color from the " aureoles " mentioned under No. 265 

 to the characteristic brown of the biotite, at the same time fading out in the opposite 

 direction to green. These aureoles have usually quite distinctly a nucleus of very 

 dark color, as if a foreign substance provoked the change or centralized it, or retarded 

 it, and that hence the aureoles are remnants of biotite not wholly converted to pen- 

 nine. The aureoles, moreover, are not always aureoles, but patches that spread 

 irregularly, sometimes shading into the brown of the biotite. 



Titanite (sphene) in small, generally roundish, light yellow grains. 



Entile, in rods, closely associated with dark, opaque grains, resembling magnetite. 



Pyrite and hematite, the latter in very small amount. The rock might be con- 

 sidered* a changed eruptive. 



Two sections examined. 



Age. Animikie. 



Remark. This rock is completely changed, but there is no apparent generation 

 of secondaiy plagioclase. There are various areas in the section occupied now by 

 sub-opaque or kaolinic substances which are perhaps the remnants of original plagio- 

 clases. N. H. w. 



No. 271. QUARTZYTE. (Graphitic.) 



" Finely graphitic quartzyte; from the same place as the last." 

 Kef. Annual Report, ix, page 65. 



Meg. A rather tine-grained, gray quartzyte. It consists of grains of quartz and 

 feldspar in a darker mass which is mostly graphite. The rock is indistinctly mottled 

 with gray or pinkish, this being due to small areas where the graphite is much 

 decreased in amount or is almost absent. 



No section. 



Age. Animikie. u. s. o. 



No. 272. BARITE, CALCITE, ETC. (Vein material.) 



From the vein on S. W. % sec. 32, T. 64-7 E. Pigeon point. 



Eef. Annual Report, viii, pages 15, 16; Annual Report, ix, page 65. 



Meg. The hand sample is a coarsely crystallized mass of calcite, barite and 

 quartz. 



No section. 



Age. Embraced in the Animikie rocks; crosses a dike running N. 60 E. 



U. S, G. 



