372 THE PENOKEE INOiST-BEARING SERIES. 



4. Jiisper-conslomcratc. Specimens 9201 (slide ;?()05), 9L'63 (slide 4486), 7418 

 (slide 1S77), GO N., (KtO W., See. 20, T. 47 K, R. 43 W., Michigan. 



The matrix of the rock is dark green, fine grained, finely laminated, has a 

 greasy feel, and contains niunerons medium sized grains of a cleavable mineral. This 

 matrix is qnitc thickly studded with fragments of red jasper, some of which are from 

 to 8 inches in diameter. 



The thin sections arc composed of finely crystalline and coarsely fragmental 

 parts. The fragmental portions comprise large, somewhat rounded areas of a finely 

 crystalline Ijasic eruptive and medium grains of feldspar, the former variety of frag- 

 ments being more abundant. These complex basic areas contain chlorite, biotite, 

 tabular feldspars, ferrite, and epidote^, and are almost precisely like the basic erup- 

 tive which is developed upon a large scale Just to the southward. The feldspar frag- 

 ments are in part orthoclasc and in part plagioclase. The abundant fine grained 

 cementing material consists of clierty silica, sm ill flakes of chlorite, and few of biotite. 

 The pebbles of the conglomerate are typical red-banded jaspers. The rocks are 

 apparently intermediate between fragmental ones and those of the noufragmental 

 iron-bearing belt. Nonfr.igmental sedimentation has begun, but it is yet accom- 

 panied with mechanical sedimentation. 



5. Clay-slate. Specimen 12580 (slide 5340), 460 N., 1010 W, Sec. 20, T. 47 N., 

 R. 43 W., Michigan. 



The rock is a light green, aphauitic, finely laminated, soft slate. 



The thin section consists of intimately mingled finely crystalline quartz, chlorite, 

 sericite, and iron oxide. Much of this (luaitz is fragmental. The sericite is a light 

 greenish-yellow, somewhat brilliantly polarizing, and is arranged in parallel rows of 

 flakes which extinguish rectangularly. If other constituents are present, they are 

 too obscure to be recognizable. 



6. Feldspathic (piartzites. Specimens 7383 (slide 1840), 000 N., 460 W.; 9244 

 (slide 4479), 0245 (slide 4480), 1100 N., 460 W., Sec. 21, T. 47 N., R. 43 W., Michigan. 



The rock varies from fiesh color through greenish-gray to dark brown ; is 

 rather fine grained, almost massive, and breaks with a subconchoidal fractnre. 



The thin section is composed largely of clastic particles of cpiartz and feldspar, 

 the former much the more abundant and often enlarged. The feldspars arc orrhoclase, 

 microcline, and plagioclase. The rather abundant interstitial material is finely crys- 

 talline (piartz, chlorite, kaolin, and iron oxide. 



7. Quartzite. Specimen 7385 (slide 1851), 900 N., 750 W,, Sec. 21, T. 47 N., R 

 43 W., Michigan. 



The rock is a greenish-gray, medium grained, compact vitreous quartzite. 



The thin section is mainly composed of enlarged fragmental grains of quartz. 

 The induration is, however, mostly due to finely crystalline interlocking interstitial 

 quartz, mingled with which is chlorite and l)rown oxide of iron, 



