THE EASTERN AREA. " 433 



separated from the fen-viginoiis graywackes and quartzites to the south and 

 nortli. 



Siniiiiiarif. — The area east of the center of T. 47 N., R. 44 W., Michi- 

 gan — or rouglil}', east of the Little Presque Lski — differs from the sinq)le 

 series described in the ])revious chapters in many important points. This 

 area was the center of great vok'anic activity ; consetpiently the sedimen- 

 tary succession inchides hu"ge thicknesses of interstratilied hiva tiows and 

 volcanic turt's, whicli are not paralleled by any rocks that are found in the 

 western area. Further, this volcanic material has greatly disturbed tlie 

 water-deposited sediments in the district, so that it is ditHcult to certainly 

 correlate the formatious east of the Little Pres([ue Isle with those west of 

 it. Another point in which this area differs from the western one is that in 

 one place the relations of the hoi-izontal P^astern sandstone to the Penokee 

 series can be made out. 



No exposures certainly belonging to the Cherty limestone member are 

 found within the area. The Quartz-slate member is not known to be con- 

 tinuous iu this area. Typical exposures of the formation, whicli have near 

 the base variegated slates, and for the upper horizon the vitreous quartzite, 

 are fcnnid at one or two localities. 



The lowest belt which certainlv is continuous for some distance is the 

 L'on-bearing member. Even in this wide gaps occur in which no exposures 

 are known. Its typical rocks are almost exactly like those of the iron for- 

 mation to the west. There is here, however, closer relations between 

 the original siderite and the actinolite and magnetite than to the westward. 

 In this respect the rocks of this belt resemble very closelv those of the 

 Animikie iron-bearing formation. The one important point in which this 

 part of the Iron-bearing member differs from tliat to the westward is that 

 mingled witli it is fragmental material. There are all gradations ljet\\een the 

 pure nonfragmental sediments of the iron belt and the fragmental material 

 of the slate formations; also there are in places interlaminations of the two. 

 It thus is clear that durin"- the time of the formation of the li'on-bearing' 

 member there were interruptions, as a result of which tlie l)elts of pure non- 

 fragmental, water-deposited sediments are alwavs narrow. Probably result- 

 ing from tliis is tlie fact that within this area no Morkaljle ore deposits have 

 3ION xis 38 



