Plate XIX. — T'bom the Quaetz-Slate Member. 



Fig. 1. Biotitic chlorite-slate. Speciuipu 9565, slide 3098. From tlie NW. i of Sec. 14, T. 44 N., R. S 

 \V., Wiscousin. lu polaiizeil liglit, x 60. Mauy small oval and angular particles of quartz 

 are contained in a matrix consisting very largely of chlorite, with which is, however, a 

 small aiuounf of liiotite. The angularity of the quartz-grains is very noticeable. This is 

 in some cases due to the enlargement of the quartz-grains, but often they were thus angu- 

 lar when de]K>sited. The tjgure has a more crystalline appearance than the section from 

 which it was taken, from the fact that the cores of the quartzes which have undergone a 

 second growth are not strongly marked otf from the enlargements, although in thin section 

 they are easily ilistinguished. (See p. 158.) 



Fig. 2. Biotite-slate. >Spe(inieu 9644, slide 3154. From the NE. i of Sec. 17, T. 44 N., R. 3 W., Wis- 

 consin. In ordinary light, x 60. A few grains of quartz with general roundish forms, 

 although now minutely angular by enlargement, are contained in a background which 

 (•ousists almost wholly of biotite and quartz. In the light irregular areas quartz is pre- 

 dominant, and elsewhere biotite. While the fragmcutal character of this rock is not 

 evident in the figiire, it is jilaiu in thin section. The rock, however, is one of the most 

 crystalline of the l)iotite-Blates which are found in the Quartz-slate member. It is wholly 

 j)ossible that the irregular whitish, roundish areas now composed of quartz auil mica rep- 

 resent original fragmental grains of feldspar. (See ji. 156.) 



Fig. 3. Sandstone. Specimen 9004, slide 2880. From the NW. i of Se<-. 27, T. 47 X., R. 47 W., Mich- 

 igan. In ludiuary light, X 60. Quartz in roundish and irregular fragmental grains, is 

 the predominatiug constituent, altliougli feldspjir is imjiortaut. I'lie abundant interstitial 

 material is so heavily stained with oxiile of iron that it is dillicult to determine what ullier 

 iiiiiuT;ils iirc present. (Seep. 163.) 



Fig. 4. Argillaifoiis shale. Specimen 7504, slide 1946. From the NE. i of Sec. 15, T. 47 N., R. 45 W., 

 Michi'^:ni. In ordinary light, x 60. The section .shows ime of tlni finer grained and more 

 clayey )>hases of the Quartz-.sl^te member. On one side of the figure recognizable frag- 

 ments of quartz and felds|)ar are the chief constituents. Upon the other side extremely 

 linely divided clayey minerals are preponderant. (See p. 167.) 



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