318 THE PENOKEE IRON-BEARING SERIES. 



sequeut separatiou of silica. These miiieial.s are not plentifully present, but are so 

 situated with respect to the feldspars as to leave little doubt of the connection 

 between them. A portion of the finer grained quartz is certainly secondary. 



20. Biotite-sehist, from west side of fault at an upper middle horizon. .Speci- 

 mens 9539 (slide 3315), lUJi Wis. (slide liUli), from 1G5() N., W., Sec. 10, T. 44 N., 

 E. 3 W., Wisconsin. 



The rocks are like 2. 



The thin sections are like those of 2. 



21. Muscovitic biotite-schists, from west side of fault at a middle horizon. Speci- 

 mens 9537 (slide 3314), 50 N., 1950 \V.; 2001 Wis. (slide 281), 30 N., 1950 W.; 2002 

 Wis. (sMe 382), 130 N., 1950 W.; 953(i (sUde 4223), J50 N., 1950 W., Sec. 2, T. 44 

 N., R. 3 W., Wisconsin. 



The rocks are gray or green, fine grained, quite massive, yet showing a more or 

 less obscure schistose structure. 



The thin section 4223 resembles very closely those of 3 and 4. It differs from 

 them in that the alterations have not gone quite so far, and consequently the original 

 fragmental nature of the rock is clearly made out. Many of the more angular graiu>' 

 of quartz are distinctly seen to be widely enlarged. In places saturating (piartz has 

 penetrated through and tlir(mgh large grains of feldspar. In this numner large sec- 

 ondary individuals of quartz have formed, no part of which is fragmental. The mica 

 is abundant and nuicli of it is secondary to feldspar, while there is little doubt that all 

 or nearly all of the biotite, niuscovite. and enlarging quartz are secondary products, 

 having resulted from decomposition of the feldspar. The section 3314 differs from 

 4223 in that the alterations of feldspar ami enlargements of (juartz are not so easily 

 traced, and in that a considerable quantity of cUorite has resulted from the decom- 

 position of the feldspar. The thin sections 281 and 282 contain numerous well rounded 

 somewhat coarse particles of quartz ami feldspar, so that they are much nearer their 

 original condition than 4223 and .3314 from the same locality. In them the altera- 

 tions of feldspar have also produced chlorite and kaolin as well as biotite and mns- 



covite. 



22. Biotite-sehist, from west side of fault at tlie uppermost known horizon, 

 134 Wr., from 250 N., W., Sec. 3, T. 44 N., R. 3 W., Wisconsin. 



The rock is like 9530 in 21, exce])t that it is very plainly schistose and in places 

 biotite is very prominent. 



In essential points this section is like 4. 



Section cast of Mellen junction. 



23. Biotitic and chloritic graywacke-slate, at a middle liorizon. Specimens 12764 

 (Slide 5459), 127(i5 (slide 54(>0), NE. i of NE. i Sec. S, T. 44 N., R. 2 W., Wisconsin, 

 on the Wisconsin Central Railroad. 



