THE EASTERX AREA. 407 



crystalline silica a large aiuouut (if brilliantly polarizing mineral in minute scales 

 and mauy brown ])articles of liydrated iron oxide. Whether this fragment is impure 

 opal or is from an altered felsite it is impossible to say. The other is an almost pure 

 specimen of chert, except that it contains many small fragmental ])articles of ([uartz 

 as though it were a nonfragmental sediment which had received a considerable ijuan- 

 tity of mechanically deposited quartz. The interstitial material of the section consists 

 of cherty silica, which contains large brilliantly polarizing flakes of sericite ami also 

 areas of brown liydrated iron oxide. This matrix includes many large, well roiiniled, 

 simple grains of quartz and few of feldspar. 



48. Recomposed granite. Specimen 12626 (slide 5375), 1730 N., 1480 W., Sec. 

 28, T. 47 K, R. 42 W., Michigan. 



The rock is chiefly composed of the coarse granite detritus, but contains some 

 seams of fine qnartzite-like material and few white quartz pebbles. The granite 

 detritus is often in large complex" fragments, but also there are present numerous large, 

 apparently simple grains of quartz and feldspar. 



The section is cut from the fine grained quartzite-like part. It consists of a 

 matrix and contained fragments in about equal quantity. These fragments are 

 almost wholly quartz, rather small, mostly well rounded, and often enlarged, the 

 enlargements fading into the fine grained matrix. Flakes of muscovite of some size 

 ai)])ear, whi(;h are taken to be fragmental. The matrix is mostly cherty (juartz, but 

 mingled wth it is a good deal of sericite, hematite, and limonite. 



4!). Sericite-schist. Specimen 12029 (slide 5378), 174S N., 1462 W., Sec. 28, T. 47 

 N., R. 42 W., Michigan. 



The rock varies from dirty yellow to brown, is finely foliated, and ujion its 

 cleavage surface has a micaceous sheen. 



The thin section is essentially like that of 44, the oidy dilference being that the 

 fragmental particles are larger, the folia of the sericite is not in short wavy folds, 

 and the section is heavily stained with iron oxide. 



50. Recomposed granite. Specimen 12818 (slide .5402), l.">()7 N., 1404 W., Sec. 

 28, T. 47 N., R. 42 W., Michigan. 



In hand specimens this rock would be taken foran ordinary granite unless it 

 were closely inspected. The eye recognizes coarse pink feldspar, translucent quartz, 

 and a green material, all being arranged so as to show a somewhat banded appear- 

 ance like a coarse gneiss. The only indications that it is different from an ordi- 

 nary crystalline rock are its somewhat nodular weathering, as though comjwsed 

 in ])art of ])ebbles, and a roundish appearance of the larger white quartz areas. 



A large part of the section consists of complex granite fragments, coiiq)osed of 

 quartz, microcline, orthoclase, chlorile, iron oxide, and other accessories. In the inter- 

 stices are finely crystalline (piartz, chlorite, and some ferrite, iu(duded in which 

 are large simple particles of (piartz and feldspar. 



