THE IKON-KEAHINC; MEMl'.lAi. 219 



Thf'sf siM'ciiiieii.s ;uf (Voiii very iic-ar I lie siiniinit <if tli« Fion-bcaririf,' lioiizoti. 

 ha\iiig IxM'ii tiikcii iiiiint'iliatfly ht-iiiMtli tlic Vfry thin siiid [XM-iiliar ^iariii'tilVMuiis rock 

 wbifb lies at the t«p i)f this ihimhIici. They arc tliinly laminated in li^'ht am! dark 

 gray shades, a)thaiiiti<;, and very rddsely resemldc the ri«-ks hist described. .Sp. gr. 

 of ft").-..-*, .•{•(i.>. 



Tiie tliin sections of these specimens pn-scnt ajipcarancc^ like tlnoc of II. 'I'l. 

 XXIII. Figs. 3, 4; I'l. XXVIII, Vit^. 4.) 



13. Magiietiti(; and garnetifeious actinolifewliists, from the summit of the Iron 

 mend>cr on the west side of Pcnokcc <i;i\>. Specimens '.•."».">.> (slide .'»18-S), from X., 

 im) W.; U04, Wis. (.slide L'41), from N., 1!K)0 W.; 1444, VVi.s. (slide liK.'J,. from 

 N., 16<I0 VV., Sec. 11, T. 44 X., 1{. .'. W., VViwonsin. 



These are dark wjiored aphanitic rock.s. Itamled vaguely with lighter streaks, 

 lia\ing a pronounce<l eonchoidal cross fracture, but cleaving readily parallel ttt the 

 lauunation. In .some places, with a stnmg magnifying glass minute individuals of 

 garnet may be dete<;ted. The.se aiijtear mo.st abundant in the light colored stieaks. 

 Si., gi. of !».>>?, .S-42. 



The thin sections are almost wholly com])Osed of magnetite. actinoliU-, and 

 garnet. The garnet is in rather small and very numerous individuals, which present 

 a ]>ale pinki.sh tint in the thin sections. In the ordinary light many of tiiem are .seen 

 to be prrjvided with crystal outlines; in the iwlarized light tlils becomes less evident, 

 bei-ause many of the garnets are j;enetrated by numerous needles of actinolite, which 

 are frequently more plentiful in tiie r(ut«'r portions of the garnet. The actinolite 

 makes up mo.st of the int<'rstitial iM>rtions of the M'ctions. but al.sti penetrates and is 

 included within the garnet iudividiiai.s. It was at first siip]»o.s4-d that this actinolite is 

 an alteration product of the garnet, but the fact of the abundance of the actinolite in 

 the immediately underlying magn«!titic and a4tinolitic .schists with whiih this garnetif 

 erous rf)ck Ls so intimately ass<H-iated. and in which the actinolite is surely not an 

 alteration product of garnet, seeming to render such an origin improbable, this view 

 was abamloned. A further study of the section seems to show that the bulk of the 

 actinolite is rather independent of the garnet, having been in part of a simultaneous 

 crystallization with it and in part of a j.revious crystallization. The magn<'tite. in fine 

 ]iarti<-les, at times erj'.stal outlineil, is s<;attered uniforndy through all portions of the 

 s4'ction, being included within all of the other minerals. Hiotite wm-ui's in numerous 

 minute Hake.s, whii-h apj/ear in all c-a.ses to l>e secondary to the actinolite individuals. 



14. Alt^Twl garnetiferous actinolite 8<^:hirtt.s, from the summit of the Iron member 

 on the west side of I'enoke*- gaj>. Spe<-imens 1.^)1, Wis. (slide 27*»), from KiTO X., 

 11(M» W.; l.Vd' Wis. rslide L'TT). from KJTO N.. IUMI W., Sec. 1 ». T. 11 N., IJ. -i W^, 

 Wi.swjnsin. 



Macroscopically the.se rocks resemble 13. 



