THE EASTERN AREA. 429 



Eastern area its equivalent is found in only two places, within a short dis- 

 tance from each othei", in Sec. 21, T. 47 N., R. 43 W., ^Michigan. So far as 

 present information goes, the Quartz-slate is now probaldy the oldest con- 

 tinuous sedimentary formation of the area, since nowliere are exposures 

 found which can be referred to the Cherty limestone, unless the ferruginous 

 limestone in the north part of Sec. 23, T. 47 N., R. 43 W., just north of 

 the large exposures of crystalline schists is to be here placed. The thickness 

 of the quartz-slate in Sec. 21 is considerable, and, as has been seen by the 

 description of the exposures (pp. 368-369), they are typical in every way of 

 the like rocks from this member to the west, and can without hesitation 

 be correlated with them. 



Following above the quartz-slate are the nonclastic sediments of the 

 Iron-bearing member. The exposures are sufficiently lunnerous to sliow 

 that there is l)ut little doubt of its continuity. It t>utcrops as far east as 

 Sec. 23, T. 47 N., R. 43 W., ]\Iichig«in, are pinv nonfragmental sedi- 

 ments. There is no evidence that the belt lias any great thickness in Sec. 

 25, T. 47 N., R. 44 W., and it is certainly not more than one-half the thick- 

 ness of the iron-ljearing belt to the west, even if tlie entire spiice l)e- 

 tween the hornblende-schists of the underlying c(im|)lcx and tlie known 

 exposures of the greenstone-conglomerate is entireh' occupied b\' this mem- 

 ber. If a part of tlie unexposed space is occupied Ijy the (puirtz-sl;ites, tlie 

 thickness of the iron-bearing- formation wcmld here be no more than a frac- 

 tion of its thickness in the western area. East of Sec. 30, T. 47 X., Iv. 43 

 W., in the south part of Sec. 20, and in Sees. 21, 22, and 23, the iron-l)car- 

 ing sediments are spread over a considerable distance north and south, but 

 here they are mingled Avitli mechanical sediments. A comparati\ely great 

 thickness of such material might be deposited in the time taken for the for- 

 mation of a thin layer of pure nonclastic sediments. If the iron-bearing belt 

 extends farther than the NW. \ Sec. 23, T. 47 N., R. 43 W., it nuist l>e exceed- 

 ingly nai'row, for tliere is but a small space between the exposure <it gi-een- 

 stone-conglomerate and the crystalline schists of the Southern ('om])lex. 



The deposition of this thin layer of nonfragmental sediment tlius 

 traced out did not go on undisturbed, for the ilow of poqjliyrite in Sees. 21) 

 and 30 is plainly interleaved. This interljedded flow of basic eruptive 



