316 THE PENOKEE IRON BEARING ISERIES. 



beeu thus decomposed, the only trace of any original i'ragmental matierial would be 

 the general oval or roundish character of the larger particles of quartz. 



IG. Biotitic and muscovitic graywacke, from west side of the fault, at a middle 

 horizon. Specimen 9.544 (slide 3092), 1105 N., 1000 W., Sec. 11, T. 44 N., R. 3 W., 

 Wisconsin. 



A gray, coar.se grained, massive rock, having a conchoidal fracture. 



Large fragmental grains of quartz and feldspar, with the alteration and replac- 

 ing products of the latter, make up the mass of the thin secrtion. The areas of quartz 

 are enlarged, and (M)nsequently minutely angular, although still retaining their general 

 roundish form. The feldsi)ar is much fresher than in 15, many individuals showing 

 no alteration intlueu(;e excei>t a little kaolinization. Other individuals, however, 

 include many grains of quartz or large reticulating cpiartz individuals with luimerous 

 flakes of muscovite. Here these minerals are plainly alteration products of the feld- 

 spar. In many cases this alteration has proceeded so far as to leave irregular cores, 

 which are entirely surrounded with the secondary (juartz, biotite, and muscovite. 

 Again in other cases the original rounded outlines of the feldspar are distinct, the 

 alterations having occurred in spots through the grains. The liner portions of the 

 rock are comi)()sed of (juartz, biotite, and muscovite, often without any feldspar. 

 These i)ortions are also probably alteration products of feldspar, the individuals jter- 

 haps being small, or at any rate are alteration ])roilucts of feldspar mingled with 

 detrital (piartz. Through the liner grained portions of the rock are numerous small 

 liarticles of black opaque material. (PI. xxxii, Pig. 2; PI. xxxm, Fig. 1.) 



17. Biotitic graywacke, ft'om the west side of fault at a middle horizon. Speci- 

 men 9545 (slide 3319), from 1100 N., 1000 W., Sec. 11, T. 44 N., R. 3 W., Wiscousiu. 



The rock is gray, coarse grained, massive, and has a conchoidal fracture. It 

 contains numerous particles of limpid (juartz and less i>lentiful ones of white or pale 

 pink feldspar, which are so large as to enable one to easily see their rounded .forms. 

 The rock in appearance api)roaches that of a gray qnartzite. 



In the thin section very large, rounded, often complex areas of quartz are very 

 numerous. These grains as to general form are well rounded, but their outlines are 

 minutely irregular, and these irregularities are doubtless due to enlargements. The 

 feldspar also is found in rounded areas. It is often more or less decomposed, the 

 method of alteration and the products produced being precisely as in 10. Contained 

 in the section are large areas composed almost entirely of finely crystalline quartz, 

 brown folia of biotite mingle<l with small remnants of feldspar, each of which with- 

 out d(mbt represents a singh^ fragmental feldsi)ar. 



18. Biotitic schists, from west side of fault at middle horizon. Specimens 9.543 

 (slide .3318), aiul 1494 Wis. (slide 273), from 1110 N., 1000 W., Sec. 11, T. 44 N.. E. 3 

 W.. Wisconsin. 



A dark gray moftIe<l, line grained, and quite massive rock. 



