402 THE PENOKEE IKON-BE AEING SEKIES. 



what i-ouuded; these are eiihiiged. Apparently also a few of the orthoclase particles 

 are enhirged. The rather abundant interstitial material is chlorite, finely crystalline 

 quartz, Hakes of kaolin or sericite, and particles of iron oxide. A few small particles 

 occur which appear to be tourmaline. 



'28. Ferro-dolomitic slate, fi-om top of belt. Specimen 1284:4: (slide 5499), 1000 N., 

 80 W., Sec. 14, T. 47 K, E. 43 W., Michigan. 



The rock is light greenish gray, ilne grained, finely lamiuated, and has the 

 appearance of an impure clayey limestone. 



Eather small i)articles of quartz, many of which are slightly enlarged, with feld- 

 spar, both of quite uniform size, compose about one-half of the thin section. This mate- 

 rial is set in a grouudmass which consists chietly of ferro-dolomite. The ferro-dolo- 

 mite is mostly in irregular reticulating areas, tilling the interstices, but many detached 

 particles have distinct rhonibohedral outlines. Mingled with the ferro-dolomite are 

 some finely crystalline quartz, chlorite, ferrite, sericite. A few small crystals of zircon 

 are seen, one of which shows finely a zonal structure. 



29. Ferrodoloiuitic slate, interstratifled with 28. Specimen 12843 (slide 5627), 

 1000 K, 80 W., Sec. 14, T. 47 N., E. 43 W., Michigan. 



The, lock diflers from 28 in being composed of alternate layers of gray and green 

 material. 



The tliiu section is not essentially dittereut from that of 28, excejjt that it contains 

 less fragnu'ntal material. Also a good many small crystals of pyrite, and uunu'rous 

 roundisli areas of some mineral which has a radial polarization (perhaps chalcedony), 

 are found. 



/Section near the centerx of Sees. 13 and 2-1^ T. 17 N'., R. 43 W., Michif/an. 



30. Chloritic slate, from near base of belt. Specimen 12591 (slide 534G), 1986 N., 

 1077 W., Sec. 24, T. 47 N., E. 43 W., Michigan. 



The rock is like 24, except that it is coarser grained. 



In thin section the minerals and their arrangement in wavy parallel lines are the 

 same as in 24. The constituents are in coarser particles, and a portion of the (|uartz 

 and feldspar are plainly fragmental. 



31. Chloritic gray wacke- slate, fnnn a lower middle horizon. Specimen 10396 

 (slide 4005), 280 N., 1500 W., Sec. 13, T. 47 N., E. 43 W., Michigan. 



The rock is like 25, except that it is coarser grained. 



The thin section differs from that of 25, in being coarser grained, and in contain- 

 ing a little calcite or some other carbonate. 



32. Gray wacke- slate, from a middle horizon. Specimen 7358 (slide 1827), 370 

 N., 1000 W., Sec. 13, T. 47 N., E. 43 W., Michigan. 



The rock is black, tine grained, almost masjiive, and has a subconchoidal fracture. 



