THE EASTERN AREA. 385 



The matrix of the rock is dark mottled green, fine giaiiied, and schistose. The 

 prevailing jjebbles are the same as those in 7. Occasionally a white (juartz pebble is 

 seen. 



The thin sections are in essential respects like those of 7, having a quartzose 

 matrix. Large fragments of extraordinary irregularity are contained in a reticulating 

 groundmass consisting mostly of finely crystalline (juartz. The (juartz runs around 

 and through the fragments in such a manner as to suggest that it is, in large part at 

 least, secondary and has dissevered the contained fragments. This is rendered prob- 

 able by the fact that the irregular outline of one fragment is often the reverse of 

 the outline of the adjoining one. The fragments are composed of green nonpolariz- 

 ing cldorite, much altered tabular plagioclases, roundish granules of titanite, and 

 abundant epidote, the latter being sometimes concentrated into large irregular com- 

 plex areas. (PI. xxxv, Fig. 2.) 



Section east and west of the line between Sec. 19, T. 17 N., R. 43 W., and Sec. 21, T. 17. 



N., R. 11 W., Michigan. 



13. (rreenstone-conglomerate. Specimen 1)350 (slide 4931), 20 N., 475 W., Sec 

 24, T. 47 N., R. 44 W., Michigan. 



The specimen does not differ from those of 2. 



The thin section combines the characteristics of .those of 2 and 12. The pebbles 

 vary in size and are closely packed together, .so that the matrix is very sparse. It 

 consists of the fine debris of the ])ebbles mingled with finely crystalline quartz. 

 A portion of the pebbles have the gray amorphous background so common in 2, con- 

 tained in which are many somewhat altered crystals of plagioclase. I'ebbles r>f 

 another class are similar to those in 12, in that they contain a large amount of epidote 

 and chlorite. 



14. Greenstone-conglomerate. Specimen 9349 (slide 3027), 425 N., 500 W., Se«. 

 24, T. 47 N., R. 44 W., Michigan. 



The specimen is not difl'ereut from the previously described greenstone- 

 conglomerates. 



Tlie thin section is cut from a schistose portion which was taken to be the 

 matrix, and is plainly a much altered, very fine grained, amygtlaloidal jiorphyrite. 

 The background now consists of gray amorphous material, much altered jilagioclases, 

 and, as secondary materials, chlorite, epidote, and small, brilliantly jtolarizing flakes. 

 The amygdules are chiefly chalcedouic quartz, but frequently associated with it are 

 chlortte and calcite. 



15. Greenstone-conglomerate. Specimen 9300 (slide 3013), 850 N., 1750 W., Sec. 

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



The matrix of the conglomerate is dark green, rather coarse grained, and 

 schisto.se. The pebbles do not difler from those of the jireviously described con- 

 glomerates. 



MON XIX 25 



