1G2 THE PENOKEE IKON-BEARIlSfCi SERIES. 



19. Ferruginous and feldspathic quartzites, from the upper horizons. Specimens 

 91.51 (slide 2802), from 310 N., 1120 W.; 91.52 (slide 3104), from 310 N., 1130 W.; 91.53 

 (slide 2803), from 310 N., 1110 W.; 9154 (slide 2804), from 3.50 N., 1132 W.; 9045 (slide 

 2885), from 395 N., 1055 W., Sec. 27, T. 4(j N., R. 2 E., Wisconsin. 



The specimens vary from those of a medium grain, vitreous luster, and con 

 choidal fracture, to those which are very fine grained and lusterless. They are 

 stained from a light to a dark brown by hydrated iron oxide. 



Rather small and well rounded fragments of quartz, now provided with inter- 

 locking enlargements, predominate in the thin sections. Fragments of ortlioclase 

 and plagioclase, commoidy quite fresh, occur in some abundance. In some sections 

 large lilms and areas of hydrated oxides of iron are plentiful between the fragments; 

 in other cases (2802) chlorite flakes occur mingled with the iron oxide. (PI. xx, 

 Figs. 3 and 4.) 



20. Quartzite, from the uppermost layers of the Quartz-slate member, being the 

 foot wall at the Bessemer mine. Specimen 9054 (slide 2920), from 1000 N., 1838 W., 

 Sec. 26, T. 46 N., R. 2 E., Wiscon.sin. 



Both macroscopically and microscopically this quartzite is exactly like 14. 



From the Germania mine section. 



21. Slaty feldspathic quartzite, from a high horizon and immediately beneath 

 9013. Specimen 9011 (slide 2700). From 133 N., 1500 W., Sec. 24, T. 46 N., R. 2 E., 

 Wisconsin. 



The rock is composed of mterstra tilled seams of a coarse pinkish quartzite and 

 a tine grained green material. 



Fragments of quartz and feldspar make up most of the section, the particles 

 Ijeing (piite angular. In the case of the quartz this angularity is plainly due to a 

 secondary enlargement. Between these fragments is nu interstitial material, com- 

 posed in part of a minutely crystalline ([uartz, with limonite, kaolin, and sericite in 

 minute flakes. The section resembles closely 2802 in 19, above described. 



22. Quartzite, from the uppermost horizon, immediately in contact with the Iron- 

 bearing member, being the foot wall of the Germania mine. Specimen 9013 (slide 

 2767). From 200 N., 1560 W., Sec. 24, T. 46 N., R. 2 E., Wisconsin. 



Both macroscopically and microscopically this rock is like 14. 



From the Ashland mine section. 



23. Slaty and cherty quartzite, from a low horizon. Specimen 7621 (.slide 2017). 

 From 1805 N., 1910 W., Sec. 27, T. 47 N., R. 47 W., Michigan. 



This rock is composed of thinly interstratifled seams of a greenish or yellowish 

 gray vitre(nis (juartzite, and of a dark green aphanitic material. 



The thin section appears to be cut wholly from one of the quartzitic seams. It 



