Till'; EASTEKN AREA. 399 



i;{. Olay-sliitc, from middle. oC bidt. Siii'cimeii T.JSS (slide 185;{), :M) N., 1980 \V., 

 Sec. !(>, T. 47 N., K. 4.? W., Micliif;iiii. 



The rock is ^riiyisli ^iieeii, apbanitic, iuul iinely sehiptosc. 



The thill section Ims a Iinely crystalline matrix consistiii}; of (|uarty., chlorite, 

 kaolin, and iron o.\ide, and contains many small tiagmental particles of (^nartz and 

 feldsjjar. 



14. Clay slate, from iipiwr part of belt. Specimen 7;38!) (slide 1854), G50 N., 50 

 W., Sec. 17, T. 47 N., K. 4;{ \V., Michigan. 



The rock is bhick, aplianitic, and easily clcavable. 

 The thin section is like that of 9. 



15. Ferro-doloniitic slate, from lower middle part of belt. Specimen 92;« (slide 

 2946), 175 X., Kilo W., Sec. 10, T. 47 N., K. 43 W., Michij^an. 



The rock i^ dark greenish gray, fine grained, schistose. Weathering gives a 

 thick outer layer of dark brown material. 



The thin section shows a gronndmass consisting of ferro-dolomite, clierty silica, 

 and chlorite, the tirst being jiredoniinant. ('ontained in this gronndmass, and com- 

 jxisiiig perliaps oue-fourth of the rock, are ]>Ientiful fragments of (jiiartz and few of 

 feldspar. Here and there minute blades of sericite or inuscovite are seen. 



10. Chloritic graywacke-slate, from middle part of belt. Specimen 7;}98 (slides 

 1861 and 2044), 500 N., 1000 W., Sec. 16, T. 47 N., K. 43 W., Michigan. 



The rock is hke 12. 



The thin section is like that of 12. 



Section in «;»/ ncio- the east half of Sec. 13, T. 17 N., R. 18 W., Michigan. 



17. (i^nartzose ferro-thdomites. Specimens 7308 (slide 1836), 7369 (slide 1837), 

 9213 (slide 3000), 9214 (slide 2937), and 9215 (slide 2938), 40 X.. 198() \V., See. 14, T. 

 47 N., It. 43 W., Michigan. 



The rocks vary in color from gray to bright brick red, are of a medium uniform 

 grain, massive, and break with conchoidal fracture. 



A matrix of ferro-dolomite composes as much as one-half of the nuiss of the thin 

 sections. In this are set well rounded particles of ijuartz and feldspar, which, on 

 account of the abundance of the ferro-dolomite, come rarely in contact witli one 

 another. The grains of quartz are as often finely complex as sim[)le. As accessories 

 occur chlorite, sericite, and iron oxide, the latter being so abundant in slide 29;>8 as 

 to heavily stain the section. 



18. Chert, interstratified with 1 7. Specimens 7370 (.slide 1838), 7371 (slide 18;i9), 

 9216 (slide 2939), 9217 (slide 2940), from 58 N., 1984 \V., to 98 N., 1940 W., Sec. II. T. 

 47 X., U. 43 W., Michigan. 



The rocks are light to dark gray, ajdianitic, have a conchoidal fracture, and some 

 of them contain galeua aud chalcopyrite. 



