THE EASTERN AREA. 431 



At or near the cessation of tlie period of \ olcanic activity, the clastic 

 and nonclastic sediments which (>verlie them l)egan to form. How far 

 upward in the Penokee succession the deposition of sediments to the 

 west had extended is not certain, Imt apparently the period of nonclastic 

 sedimentation of the iron-beai'ing Ijelt had not ceased, as is indicated 

 by the nature of the fragmental rocks north and east of the greenstone- 

 conglomerates. In the northwest part of Sec. 15, T. 47 N., R. 43 W., 

 Michigan, are unmistakable typical nonfragmental sediments, separable 

 from similar sediments in .Sec. 16 by an almost mountain mass of diabase. 

 Exposures in Sees. 13 and 14, T. 47 N., H. 44 W., Michigan, and in Sec. 18, 

 T. 47 N., R. 43 W., Michigan, might full}- as well be classified with the 

 nonfragmental sediments of the iron-ljearing belt as with any other forma- 

 tion. From Sec. 18, T. 47 N., R. 43 W., Michigan, to the easternmost 

 exposure known iu Sec. 28, T. 47 N., R. 42 W., Michigan, the rocks are 

 quite largely nonclastic ones, Avhich contain a considerable portion of iron, 

 either as a carbonate or oxide. This is particularly true of the more southern 

 exposures of the belt, but such materials are also found in the most northern 

 exposures known, near the east tpiartei- post of Sec. 14, T. 47 N., R. 43 W., 

 Michigan. 



Above the feiruginous and fragmental slates north and east o{ the 

 greenstone-conglomerates, followed probably fragmental rocks which were 

 the equivalent of the rocks of the Upper slate belt of the Penokee succes- 

 sion ; but if this was the case such material was removed by erosion, and 

 then followed the unconformably overlying Keweenaw series. 



Before the Eastern sandstone at the east end of the ai-ea, su))se(juently 

 described, was deposited, the three series of the district were tilted into 

 their present inclined position, and during this time or later underwent 

 great erosion. That the Eastern sandstone is in direct contact \\itii the 

 Eastern area rocks near their base at Gogebic lake, is simply due to the 

 fact that these rocks were more resistant than the Keweenaw and upper 

 Eastern area rocks, and have been left as a cliff against which the 

 Eastern sandstone was deposited. How much more Avidespread than 

 at present the sandstone has been, we have no means of knowmg. 



