THE EASTERN AREA. 371 



a portion of tliem some of" the quartz is in siiuill ronnrlisli areas which 

 have an unmistakable frag-mental character. Further, all of the character- 

 istics of the rocks, both in hand specimen and thin section, are those of 

 compact clayey sediments, which in all prol)ability they are. 



TABULATION OF PETROGEAPHICAL OBSERVATIONS.' 



1. Ferniginoxis and foldspatliic conglomerate. Specimeu 9295 (slide 3012), 150 

 N., 1750 W., Sec. 19, T. 47 N., R. 43 W., Michigan. 



The rock is dark gray and massive, and the matrix is medium grained. The 

 contained pebbles are jasper, white quartz, and green schist. They are mostly small, 

 altliough occasionally one 10 inches in diameter is found. 



A thin section from the matrix shows fragmeutal [tarticles of ([uartz und feld- 

 spar of quite uniform size, the former composing jjcrliajis four-tifths of tlic section. 

 The grains of (|uartz are ofteu enlarged, and some of them are finely complex. The 

 feldspar is orthoclase, microcline, and plagioclase. Its grains are iu part fresh, aud in 

 part also nuich kaoliuized or partly altered to chlorite. In the interstices are finely 

 crystalline quartz, dark brown iron oxide, and green cldorite. 



2. Ferruginous aiul feldspathie (juartzites. Specimens 7430 (slide 1S91), 7437 

 (slide 1892), 1950 N., 1420 W.; 92S5 (slide 2902), 92S6 (slide 2903), 1975 N., 1350 W.; 

 9287 (slide 3008), 1940 N., l.!90 W., Sec. .30, T. 47 X., R. 43 W., Michigan. 



The rocks are dark gray to black, medium grained, aiul vary fro^n massive to 

 schistose, the darker colored specimens containing much oxide of iron. 



In each of the thin sections the mineral constituents are the sa :ic as in the pre- 

 vious number, the only dififerenee between the various sections being relative propor- 

 tions of the minerals contained. Slides 1891 and 2902 have dark l)fown ferrite in a 

 continuous ramifying sheet iu which the other minerals are buried. In slides 296.5 

 and 3008 the oxide of iron is nuich less in ([uantity, while the fragments of fehlspar 

 and quartz in them are abundant. The grains of fragmental ([uartz are frequently 

 enlarged. 



3. Sericitic graywacke. Specimen 9284, (slide 2901), 300 N., 500 W., Sec. 19, T. 

 47 N., R. 43 W., Miclugan. 



The rock is dark gray, fine grained, schistose, and cleaves readily along the 

 ]ilaue of schistosity. 



Rather small clastic particles of (puirtz and feldsi)ar, the fornua- lacpondciant, 

 compose tliree-tburths of the thin section. Tlu^ interstices are filled witli finely erys- 

 lalline ((uartz, kaoUn or sericite, chlorite, dark brown ferrite, and iilentiful grains of 

 bhick lustrous galeuite. 



'Till- iiiuiilii'is III' spi'ciiiiciis anil sliili's an- tliiisi' of tlie CDllrctiini of Hn- Lake, Sii])erior division. 

 Locations aro ^ivou from tin- soiUlicast coruur of tliu sections lu steps of J, 000 pir mile. 



