THE EASTEHK AREA. 387 



Exposures near corner of Sees. 11, 15, 22, 23, T. 47 A'., B. 13 W., Michigan. 



20. Greeiistoue-couglomerate-s. Siiefimeu 0227 (slide 2944), 1985 N., 170 W.; 

 7377 (slide 204;5), 1!>9() N., 180 W., Sc. 22, T. 47 N., R. 43 W., Micliigaii. 



Tlic iiuitiix of the rock i.s dull gray, in }daee.s heavily iron stained, aphanitic, 

 and sometimes slaty. The apparent i)ebbles resemble very closely the matrix in 

 which they are contained. 



The thin sections are vesy fine grained and obscure. They appear, however, to 

 contain large illy defined fragments, derived from a tine grained i)orphyrite, which are 

 mostly composed of gray material containing minute tabular plagioclases. These 

 fragments are set in a matrix, the chief constituent of which is quart/., but which 

 also contains abundant ntaterial like that com](osing the fragments. 



21. Greenstone conglomerate. 8pecimens !»222 (slide 2042), 0223 (slide 3002), 

 9225 (slide 2043), 7375 (slide 1843), 1070 N., 1640 W., Sec. 23, T. 47 N., R. 43 W., 

 Michigan. 



The matrix of the rocks is dark green and thinly foliated. The i)ebbles are in 

 part of the pale green sort found in the ]>reviously described c(mglonierates, while 

 some of them are coarser grained than usual and have the characteristic appearance 

 of massive basic eruptives. 



The matrix consi.sts, as in several cases before, of finely crystalline quartz, 

 mingled with the debris derived from the basic fragments. The fragments vary in 

 size from this fine material to large bt»wlders. Some of the smaller fragmental 

 areas are almost completely altered to chlorite and gray material, but the roundish 

 forms which they still retain probably represent original fragments. The larger 

 pebbles are plainly from basic eruptives. The coarser ones consist of greatly altered 

 plagioclase, gray leucoxene, chlorite, and blades of actinolite or hornblende, the 

 latter being plainly of secondary origin. At times the.se hornblende blades are so 

 large as to include many particles of the other minerals of the pebbles, even con- 

 taining .so much foreign material at times as to make a single individual of horn- 

 blende ajtpear in section as detached areas. 



SECTION IV.— FRAGMENTAL AND FERRUGINOUS ROCKS NORTH AND EAST OF 

 THE GREENSTONE-CONGLOMERATES. 



Geographical distribution. — North and east of the greenstone-conglom- 

 erates occurs a continuous wide belt of fragmental rocks, which extend 

 from neai- the north quarter post of Sec. 14, T. 47 N., R. 44 W., Michigan, 

 to the center of Sec. 28, T. 47 N., R. 42 W., Michigan, a distance of about 

 1 1 miles. Through T. 47 N., R. 43 W., Michigan, this belt runs in a nearly- 

 east and west direction, and probably has a siu-face Avidth through this town- 

 ship of aboitt li miles. West of T. 47 N., R. 43 W., Micliigan, the few 



