THE EASTERN AREA. 309 



rocks similar, l)ut their arrangement witli reference to each other is the 

 same as those to the west. The southernmost hiyers are green an<l hiown 

 variegated slates interleaved with layers of fine grained vitreous feldspatliic 

 quartzite, just as shown l)y the lower layers of the quai"tz-slates at the 

 typical localities of Tylers fork, Potato river, and the west luanch of the 

 Montreal. Above these variegated slates are thick beds of coarse vitreous 

 quartzite which outcrop in bold exposure. A very short di.stance north of 

 the quartzites test \nrs have shown that the iron-belt rocks occur. Thus 

 far at this point we have the typical Peuokee succession, but test-pitting 

 shows, as heretofore explained, that the ii-on-bearing rock.s* are mingled to 

 a greater or less extent with fragmental material. East and west of Sec. 

 21, T. 47 N., R. 43 W., Michigan, are fragmental rocks, which are, however, 

 not a separate belt below the iron formation, but are intercalated with its 

 uonfragmental sediments. 



I'etrogmphiad charartci-. — It is not practicable to separate these frag- 

 mental rocks into shar[)ly defined divisions, as the different phases grade 

 into each other h\ insensible degrees. TheA' can be somewhat arbi- 

 trarilv divided into quartz-slates including quartzite, and ferruginous feld- 

 spathic (piartz-slates. As to this first division nothing more need be said, 

 as \\\ii\ are precisely like rocks of the same name in the Quartz-slate mem- 

 ber to the west, "^rhe second division c^)niprises the following varieties: 

 Ferruginous and feldspatliic ipiartzite, sometimes conglomeratic, jasper- 

 conglomerate, and ferruginous chlorite-slates. 



The ferruginous feldspatliic (|uartzitcs difi'er from the (puutzites found 

 in the main (piartz-slate area to the west in that tliev contain a very 

 large amount of ii-oii oxide, wiiicli is mostly hematite, Itut mingled with 

 linionite and some magnetite. In some specimens the licmatite is s(t 

 abundant as to form a continuous ramifying sheet in which is l)iu'ied the 

 worn fragments of cpiartz and felds])ar. These fragments at several 

 exposures are .so large as to class the rock as a conglomerate. 



The exposures .shown by the test pits in the south part of Sec. "20, T. 47 



X., R. 43 W., Michigan, are of ])eculiar interest because of their relations to 



tlie underKing eruptive, and the great likeness under the microscope of 



some of them to a large part of the greeustoue-couglonierate, to be later 



MoN XIX ^ 24 



