THE EASTERN AREA. 373 



8. FeiTUffiiious and chloiitic slate. .Specimens 740(1 (slide ISO.")), 1140 N., .").')0 

 W.; 924S (slide 44S1), 1170 N., .510 W., Sec. 21, T. 47 N., R. 4;3 VV., Micliisaii. 



The lock is of a i)eculiar liistiotis hrowiiisli >>ic(mi ciilor, mottled with iriesular 

 patches of a dull brick-red color, is Hiiely laminated and very soft. 



Ill thin section, a ipiartz background contains abundant pale green chlorite, 

 brown iron oxide, red hematite, and numerous scales of a brilliantly polarizing min- 

 eral w liich is taken to be sericite. 



y. (Miloritic and biotitic slate. Specimen 73SC (slide l'04,'>), 9.50 N., 8<H) W., 

 Sec. 21, T. 47 K, R. 43 W., Michigan. 



lu tbiu section, a finely crystalline (|uartzose gTouuduiass contains a felted mass 

 of tibrous somewhat iron stained chloiitc and liiotite, the til)ers<(f which are arranged 

 iu a common direction, and give the rock a strong schistose character. Scattered 

 through this tine material are a few small grains of |)laiiily fragnieiital ((uartz. 



10. Ferruginous and chloritic slates. S|)ecimens 7.'5!t!) (.slide lS(5li), 1130 N., fjL'O 

 VV.; 7401 (shde 1804), 1200 N., 4S0 W.; 9249 (slide 4482), 1210 N., 450 W., Sec. 21, T. 

 47 N., R. 43 W., Michigan. 



The rocks are dark green, thinly foliated, and have a soft greasy feel. 



In thin section the rocks differ from 8 chiefly in that they have no hydromica, 

 and contain (piite plentifully small grains of plainly fr:igiiieiital (|uartz, which stand 

 out sharply from the groundmass. ISoth hematite and linioiiite are plentiful. 



11. Ferruginous quartzite. Specimens 9252 (slide 4484), 925;i (slide 4485), 1315 

 N., 570 W., Sec. 21, T. 47 N., R. 43 W., Michigan. 



The rocks are greenish to reddish gray, massive, and vitreous. 



The thiu sections are almost wholly composed of interlocking large grains 

 of (piartz. Films of iron oxide are found in the interstices and between the cores 

 and enlargements of the cpnirtz grains. 



12. Feldspathic ([uartzite. Specimen 125SS (slide 5;;43). l.{12 N., 1790 W., Sec. 

 22, T. 47 N., R. 43 W., Micliigan. 



The rock is gray to pink, fine grained, vitreous. 



The thiu section is chietiy composed of rather small originally well rounded 

 pai'ticles of quartz and fcldsi)ar of remarkably uniform size. The (piartz is several 

 times as abundant as the feldspar. The grains are sometimes liuely complex and 

 often ])lainly enlarged. The felds))ar com|)rises orthoclase, niicrocline, and jdagioelase, 

 all quite fresh, although a few of the grains have been affected by decomposition. 

 Between the clastic particles are found finely crystalline sihca, niimeious small well 

 defined brilliantly polarizing flakes of kaolin or sericite, and a few jtarticles of ferrife. 

 The section also contains a few grains of each of.the minerals zircon and tourmaline, 

 fhe former at times showing its characteristic zonal structure. These minerals are 

 rounded, and must be clas.sed as fragmental constituents rather than as indigeuons in 

 this rock. 



