THE IRON-BEARING MEMBER. 217 



From the Mnrenyo rii-cr imn ramje, Sec. x'3, T. II X., It. -7 H'., Wisconsin. 



7. Magnetitic actiiiolitic schist. Hpecimeu 180 \Vr. ; tVom ]!)(»0 N., 1325 VV., Sec. 

 23, T. 44 N., R. 5 W., Wisconsin. 



All ;iiilianitic, dark gray, slaty rock, so excessively (ine ifrained tliat tlie mag- 

 nifyiug glass detects none ol' its constituents. 



The thin section is mainly made \\\t ofinterlnced, often radiating, blades ofactino- 

 lite, witliin wbicli are included niunerous crystals and i)articles of magnetite. The 

 particles of the latter mineral are also at times aggregated into bunches of some size. 



8. Magnetiticactinoliteschist. Specimen 180 Wr.; from 500 N., 500 W., Sec. 23 

 T. 44 N., R. 5 W., Wiscon.sin. 



A dark gray, nearly aphanitic rock, showing on the weathered portions very thin 

 and regular lamination. The magnifying glass can barely detect the magnetite 

 particles and minute needles of actiuolite. 



Tlie thin se<'tion is similar to that of 7, save that the actiuolite is in larger blades 

 and that the rock contains a larger proportion of magnetite. 



Frum the e.rpo.siires in Sec. 31, T. 44 N., R. 4 W., Wisconsin. 



9. Actinolitic and magnetitic (piartz schist, from a low horizon. Specimen 9649 

 (slide 3159); from 1(337 N., W., Set;. 24, T. 44 N., R. 4 W., Wisconsin. 



This rock closely resembles 2 and 4, being composed of dark colored, strongly 

 magnetitic bands and light colored, quartzose, ones. 

 The thin section of this rock is similar to that of 4. 



From the e.rpositres in Sec. !), T. 44 ¥., R. o W., Wisconsin. 



10. Actinolitic and magnetitic ([uartz-schists, from a middle horizon. Specimens 

 9641 (.slide 3151), fnmi N., 400 W., and 0(!42 (slide ;?1.52), fiom N., .500-600 W., 

 Sec. 9, T. 44 N., R. 3 W., Wisconsin. 



These rocks, again, are closely like 2 and 4, ha\ing the same interhiiniiiation of 

 lighter and darker materials. The darker colored bands are \ery lich in ni.i^iietite, 

 quite aphanitic, and have a conchoidal fracture. Sp. gr. of magnetite seam in 9lil2,4-54. 

 The thin sections show a groiindmass of minutely crystalline (ptartz, the indi- 

 viduals for tiie most part interlocking with one another more or less (lec])ly, though 

 some of the more minute ones are ])rovided with crystal outlines. Tiiis groundinass 

 in slide 3152 conqtoses two-thirds of the rock; in 3151 less than half. .Magnedte is 

 scattered through the groundinass in niinuTons minute grains and crystals, which are 

 included witliin the (piartz individuals. These are .so abundant in 31.52 as to make 

 up a half of the whole section. Actiuolite occurs in a few blades wliich are heavilj' 

 stained with iron oxide and traverse the groiindmass in such a manner that each 

 blade cuts a number of quartz indi\ iduals. 



