386 THE TENOKEE IRON BEARING SERIES. 



The thin si'ctiou is like those of 12, except that tlie <|uartzose background is 

 finer grained. 



16. Greenstone-conglomerate. Specimen 7451 (slides 190.5 and 21.53), 000 N., 

 850 W., Sec. 24, T. 47 X., R. 44 W., Michigan. 



The rock varies from dark grayish green to dark green, is schistose, and weathers 

 to a dirty yellowish brown color. 



In thin seftion the matrix of the (conglomerate is very fine grained and schistose. 

 It consists of ttnely crystalline quai-tz and the debris of basic eruptives, including 

 chlorite, epidote, and brilliantly polarizing needles arranged in parallel lines. The 

 fragments vary from those of large .size, which are very plainly altered porphyrites, to 

 minute altered particles which are lost in the contained matrix. Epidote is plentiful 

 in all parts of the section. 



17. Greenstone conglomerates. Specimens 7447 (slide 1000), 1925 N., 1000 W.; 

 9.311 (slide 4928), 1950 N., 1.350 W., Sec. 24, T. 47 N., R. 44 W., Michigan. 



The rock is dark mottled green, roughly schistose, and contains numerous small, 

 vaguely outlined pebble-like areas. 



These sections do not differ materially from those of 12. 



With the naked eye the well rcjunded outlines of the i)ebbles are clearly 

 distinguished from the matrix in which they are contained. The background 

 microscopically consists of quartz (nnich of which is chalcedonic), chlorite, epidote, 

 and gray amorphous material. The large i)ebbles have a background consisting in 

 about equal ]troportion of gray material and i)ale green nonpolarizing viridite, which 

 contains greatly altered plagioclases and finely crystalline secondary quartz. 



Exposures in the east j)art of Sec. 30, T. 47 N., R. 13 IV'., Michigan. 



18. Greenstone-conglomerates. Specimens 9242 (slide 2949), 050 N., 025 W.; 

 9239 (slide 4025); 0241 (slide 2948), 920 N., 920 W., Sec. 20, T. 47 N., R. 43 W., 

 Michigan. 



The rocks are like 2, except that the matrix is distinctly schisto.se. 



The thin sections are like those of 2 so far as the fragments are concerned, )mt 

 the matrix consists, aside from finely crystalline quartz, of the fine debris derived 

 from the basic fragments. 



19. Greenstone conglomerate. Specimen 7415 (slide 1874), 1075 N., 35 W., Sec. 

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



The specimen is like 2. 



The section is from a pebble of the conglomerate. It is a fine grained, amygda- 

 loidal porphyrite, having a gray, nearly amorphous background, wliich contains 

 greatly altered plagioclases, epidote, kaolin, and some calcite. Frequentlj' the epidote 

 is contained in the plagioclase and clearly is secondary to it. A large amygdule con 

 tains a core of epidote, which is surronndetl by an aggregate of pale green chlorite- 



