THE EASTERN AREA. 435 



recomposed granitic rocks, which coiisist of firmly receniented granitic 

 debris and are separable from the original rocks only by an examination of 

 the thin sections. 



The eruptives of the Eastern area are in several detached exposures, 

 some of them being of large size. x\ ])ortion of them are jtorpln rites con- 

 temporaneous with the rocks of the series in which they are found; others 

 have the structure of a diabase, or even tliat of a gal)))ro, and these are 

 taken to be deep seated rocks. Between these two extremes there is found 

 in various parts of the area intermediate phases. The augite of the 

 diabases has often altered to lioridjlende, and this secondary hornblende 

 has undergone a new growth. Also, the unaltered augite is not infre- 

 quently surrounded b}' a sheath of suiaragdite, the crystallogra})liic rela- 

 tions of the original and secondary minerals being tho.se known to occur 

 between augite and amphibole paramorj)liic after it. 



The rocks of the various belts of the Eastern area, with the exce])tion 

 of the greenstone-conglomerate, correspond closely in lithological characters 

 with those of the Penokee series proper to the westward, the only differ- 

 ence of importance being that in the Eastern ai'ea there is more fre- 

 quently found mingled nonfragmental and fragmented sediments. The 

 greenstone-conglomerates bear such structural relations to the sediments 

 Avhich certainly belong to the Penokee series, are mingled with them so 

 intricately, and are so certainly surface volcanic accumulations, that there 

 is no sufficient reason for placing them elsewhere. 



The stratigraphical evidence that the Eastern area rocks belong to a 

 series separated both from the Southern Complex and from the Keweenaw 

 series is precisely like that which proves the clastic formations to the ^\•est 

 to belong to a distinct series. Notwithstanding the exceptional width of 

 the Eastern area in certain parts and the southern dips which are found 

 in the slate belt north of the greenstone-conglomerates, it is believed that 

 the succession here is probably a simple conformable one. 



The sequence of events in the district seems to have been as follows: 

 As in the m;un area, the complex of schists, gneisses, and granites, and 

 probably the series to which the Cherty limestone belongs constitute a b;ise- 

 meut upon whicli the Penokee succession was dcjiositcd. In certain places 

 rocks wliicli are the. equivalent of the Quartz-slate member were deposited. 



