366 THE PENOKEE IRON-BEARING SERIES. 



at the base of the beh itself we have no proof that there is a continuous 

 layer of feldspathic quartz-slates, as is the case to the west. 



It is, then, improbable that the eastern area will in the future he found 

 to contain large ore deposits although small ore-bodies may be fouml. 

 This improbability, arrived at inductively, is still further reenforced by 

 the fact that extensive explorations throughout its whole extent have failed 

 to find a single workable ore deposit. ' 



TABULATION OF PBTROGRAPHIOAL OBSERVATIONS.' 



1. MagTietitic, sidcritic, aud actiiiolitic slate. Spccimeus 12690 (slide .'"i416), 

 12697, (slide 5417), 1000 N., 1850 W., Sec. 23, T. 47 N., R. 44 W., Michigan. 



The rocks are dark gray to black, mostly fine grained, laminated, tbe lighter 

 colored l)elts Ijcing coarser grained than the others. 



In thin sections a backgronnd of finely crystalline interlocking qnartz i-ontains 

 abun<lant magnetite, siderite, actinolite, and some hematite. Both the magnetite and 

 siderite, in certain belts, exclnde the other minerals. The light gray belts seen 

 macroscopically are very largely siderite. These sections illustrate the simultaneous 

 occurrence of (jnai'tz, magnetite, hematite, actinolite, and siderite, as well as any thin 

 sections from the Penokee district. The magnetite and actinolite are closely associated, 

 as is usual in the actinolitic slates; also in tlie almost solid masses of siderite; 

 wherever quartz occurs, actinolite is abundantly present. The quartz is mostly in 

 vein-like forms as though it were a secondary mineral. This association of actinolite 

 with the (juartz suggests that the entrance of silica was necessary in order that the 

 actinolite might form. Tiie quartz in slide 5417 difl'ers iVom that found in any other 

 section of the series in that the individuals are several times longer than broad. The 

 elongation of the grains corresponds to the banding of the rock. This arrangement 

 and interlocking of the quartz graius are those of a uuich squeezed crystalline schist. 



2. Magnetitic actinolite rock. Specimen 10403 (slide 4494), 1164 N., 1779 W., 

 Sec. 23, T. 47 N., R. 41 W., Michigan. 



In thin section, an interlocking felted mass of actinolite, stained red by hema- 

 tite, contains numerous crystals and areas of magnetite, the projecting edges of, 

 which show crystal outlines. A little finely crystalline quartz is also included. 



3. Ferruginous actinolite-schist. Specimens 9354 (sbde 3308), 9355 (slide 3119), 

 9356 (slide 3268), 3()(» N., 1500 W., Sec. 25, T. 47 N., E. 44 VV., Michigan. 



The rocks are dark green, fine grained, banded, and magnetitic. 



' The nnmhers of snecitnc.iis :ui(l slides are those of the eollecfioii of the Lake Superior division. 

 Locations are given from the southeast corner of the sections iu steps of 2,000 per mile, 



