^ 



216 THE PKNOKEE IRON-BEARING SERIES. 



3. Miiguetitic ncliuolite-schist. Specimen 9(J9fi (slide 3170) ; from G'2() N., 380 W., 

 Sec. 26, T. 44 N., R. i; W., Wisi-ousin. 



This rock is cilosely similar to 2. 



The tliin section shows a backs'roand ot minutely crystalline qnartz. Traversing 

 this backgronnd are numerous blades ot actinolite, which are often arranged in rosette 

 form. The individual blades of actinolite earh frequently traverse several quartz 

 individuals, but thei'e are also seen included within single qnartz grains a number of 

 minute actinolite needles. Magnetite occurs in minute particles within the actinolite. 

 But little biotite and cljlorite, secondary to tiie actinolite, are present. 



From ihi' Atkins lahr irou vaiuje. 



4. Actinolitic and mugnetitic (luartz-schist, from a lower horizon than 5. Spec- 

 imen 9680 (slide 3167); from 6i:5 N., 6^0 W., Sec. 20, T. 44 N., R. 5 W., Wisconsin. 



This rock is very clo.sely like 2, differing only in being .still finer in grain and 

 more qimrtzose. 



The thin, section siiows a background of intricately interlocking completely 

 crystalline quartz, within which are included numerous concretionary areas composed 

 of magnetite, actinolite, and quartz, the former at times being predominant. Within 

 these areas the magnetite and actinolite particles show a tendency to an arrangement 

 in curving concentric lines w hich traverse tlie ([uartz indi\ idnals inditfcrentl>'. The 

 ininei'als between the concretions are not different fnnu tliosc that compose them, only 

 the quartz is greatly jtredominant and more coar.sely crystallized. Many of the larger 

 mostly interstitial grains of (puirtz run over into adjacent concretions Just as though 

 they were not there, tlicn iiu'lnding the bands of actinolite and magnetite. Tlie con- 

 cretions have strongly the appearance of being painted on a quartzose background. 

 No .section could present better eviilence that the quartz was the last mineral to 

 crystaUize than does tliat i>f tliis rock. (PI. xxiv. Fig. 2.) 



.->. Magnetitic actinoliteschist, from a liigher horizon than 4. Specimen 9684 

 (slide 316S); from 1340 N., .{.iO W.. Sec. 1^0, T. 44 N., R. 5 W., Wisconsin. 



The rock resembles 2, except in being darker in color, richer in magnetite, and 

 tiner in grain. Sji. gr., 3-4.'i. 



The thin section is like that of 2. 



6. Magnetitic and actinolitic quartz-.schist, from a higher horizon than 5. Speci- 

 men 9692 (slide 3169); from 400 X., 1000 W., Sec. 16, T. 44 N., R. o W., Wisconsin. 



A very conq)act rock, conq>osed of vaguely defined lighter and darker colored 

 bands, the latter so ricli in magnetite as t(» give a metallic luster. The lighter (;olored 

 ones are seen witli tlie magnifying glass to contain more (piartz. »Sp. gr., 3-4(i. 



The gronijdmass is conqjosed of finely crystalline quartz. Magiu>tite particles are 

 scattered generally tliiuugli the gronndmass, but are also often grouped in irregular 

 outlined clusters. .Vctinolitt-, with its alteratinn product, chlorite. ocTUrs as in 2. 



