368 THE PBNOKEE IRON-BEARING SERIES. 



The thin sections contain a matrix of siderite, with some (luaiitity <>f finely crys- 

 talline qi^artz, in which are buried plentifully rather small fragmental grains of quartz 

 and numerous areas of pale green fibrous chlorite. A little brown iron oxide and 

 magnetite arc found. These sections arc intermediat(i between tiie nonfragmcntal 

 rocks of the iron-bearing belt and the fragmental slates, and might with almost cijual 

 propriety be classed with one division as with the other. 



0. Hematitic chert. Specimen 7402 (slide 1865), 1320 N., 615 W., Sec. 21, T. 47 

 K, R. 43 W., Michigan. 



The rock is red, aphanitic, and breaks with a conchoidal fracture. 



The thin section is composed mostly of finely crystalline quartz. This includes 

 hematite in finely disseminated particles and in areas of considerable size. The iron 

 oxide and chert are arranged to quite an extent in more or less perfect concretioiis. 



10. Siliceous hematites. Specimens 7384 (slide 1850), 1000 N., 75 W., 9250 (slide 

 4483), 1210 N., 450 W., Sec. 21, T. 47 N., R. 43 W., Michigan. 



The rock is a cherry red and black, banded, nearly pure hematite. 



In thin section, a continuous ramifying mass of hematite contains numerous 

 complex clierty areas. 



SECTION II —FRAGMENTAL ROCKS SOUTH OF THE GREENSTONE-CONGLOM- 

 ERATES. 



Geoffraphical distribution. — Soutli of the Iron-bearing member, tln-ough- 

 out all the main area and constituting one of" the most characteristic 

 features of the Penokee series, is the Quartz-slate member. The eastern- 

 most exposure of these slates in this area is in the north part of Sec. 21, 

 T. 47 N., R. 44 W., Michigan. East of this point there is a break of about 

 4 miles, whicli, so far as at present known, is not bridged by a single 

 exposure of a j)lainly fragmental rock referable to this belt In the south- 

 -west part of Sec. 11), T. 47 N., R. 43 W., the first exposure east of the 

 Little ?resque Isle is found whicli can be regarded iis tlic equivalent of 

 the Quartz-slate member. From this point, running somewhat north of 

 east to the northwest part of Sec. 23, T. 47 N., R. 43 W., are quite ninner- 

 ous exposures south of and mingled with the iron-bearing belt which have 

 in places great likeness to or even lithological identity with the Quartz- 

 slate formation to the westward. In Sec. 21, T. 47 N., R. 43 W., just east 

 of the Presque Isle river and in the east part of the section, occur large 

 exposures of slates and quartzites which in every wa}^ nre lithologically 

 like the feldspathic quartz-slates of the main area. Not oidy are these 



