170 THE PENOKEE IKON-BEARING SERIES. 



Fr<»)i the exposures in Sec. 17, T. 47 N., R. 44 W., Michigan. 



' 53. Fel(lsi)iitliic' quartzites and quartz-slates, fi-omneai' the bottom of the Quartz- 

 slate member. Specimens 9410 (slides 3125 and 3271), 9411 (slide 3052), from 525 N., 

 1925 W.; 9389 (slide 3043), from 350 N., 1.550 W.; 9390 (slide 3044), from 350 N., 1550 

 W., Sec. 17, T. 47 N., R. 44 W., Michigan. 



Some of these specimens are slaty, while others are more quartzitic and vitreous. 

 The color varies from gray to black, being in places mottled with red spots. 



The thin sections are made up of fragments of (piartz, feldspar, chert, and jasper. 

 The quartz fragments are usually widely eidarged; the cherty and jas])cry ])ieees 

 seem in the main to represent the chert of tlie limestone belt immediately below. 

 There are, however, a good many fragments which appear to bo intimate mixtures of 

 chhirite, minutely crystalline quartz, ferrite, and a koalin-like mineral. These may 

 possibly be altered feldsjiars. The sparse matrix is very heavily stained with brown 

 iron oxide. 



54. Chloritic slate, from near the base of the Quartz-slate member. Specimen 

 9409 (slide 3051), frcmi 525 N., 1925 W., Sec. 17, T. 47 N., R. 44 W., ^Michigan. 



An aphanitic light green slate or shale, cleavable into thin ])latcs i)arallcl to the 

 lamination. 



The thin section shows an intimate mixture of an exceedingly iniimti'ly crystal- 

 line quartz, with Hakes of i)ale green chlorite. 



55. Olay-shales or clay-slates, from near the base of tlie Quartz-slate member. 

 Specimens 9391 (slide 3045), from 350 N., 1550 W.; 9412 (slide 3053), from 525 N.-, 

 1925 W., Sec. 17. T. 47 N., R. 44 W., Michigan. 



These arc fine grained and finely laminated slates or shales ; 9412 is gray, and 

 9391 leddish purple. The latter shows plentifnl flakes of sericite. 

 The thin sections of thes'e rocks are closely like those of 42. 



56. Graywackes and chloritic slates, from a low horizon. Specimens 12GG7 (slide 

 5391), 12008 (slide .-)392), from 15 N., 05 W.; 12009 (slide .5303), from 78 N., 42 VV.; 

 12f570 (slide 5394), from 100 N., 105 W., Sec. 17, T. 47 N., R. 44 W.. Michigan. 



These specimens range from slaty to more massive kinds, varying in coloi- Mir( ingh 

 dark green, reddish, dark brown, gray, and greenish shades. All arc ajihanilic. 



The thin sections show that they are of the typical slate of the <,>nartz-slate 

 member, being composed of fragments ot quartz and feldspar, buried in the usual 

 argillaceous matrix, in which chlorite, kaoliji, sericite, and a minutely crystalline 

 quartz are recognizable. 



57. Feldsjiathic quartzite or graywacke, from a middle horizon. Siiccimcii 9394 

 (slide 3122). From 470 N., 975 W., Sec. 17, T. 47 N., R. 44 VV., Michigan. 



A coarse grained, greenish gray, vitreous quartzite. 



The thin sc^ction of this rock is closely similar to 2016 in 24. 



58. Chloritic slate, from a high horizon. Spccinien 12682 (slide 541(4). From 477 

 N., 790 \V., Sec. 17, T. 47 N., R. 44 \V., Michigan. 



