GEOLOGY OF CENTRAL MINAS GERAES, BRAZIL 359 



observed facts connected with the formation of the Itabira iron 

 beds better than any other yet suggested, and to encounter fewer 

 serious difficulties. 



Like the schist and quartzite, the Itabira iron formation is a 

 true primary sediment/ It is a mixture of iron oxide and quartz 

 sand laid down essentially as it occurs today. The principal 

 change which it has undergone since its deposition is the dehydra- 

 tion which has converted the ferric hydroxide originally laid down 

 into ferric oxide, or hematite. This dehydration, like the meta- 

 morphism of the shale into Batatal schist and the sandstone into 

 Carafa quartzite, probably is to be associated with the intense 

 deformation which these strata suffered during the mountain- 

 forming movements which antedate the Devonian. 



The Itabira iron formation takes its name from Itabira Peak, 

 near the town of Itabira do Campo, a rather striking mountain of 

 splendid specular hematite which forms a conspicuous landmark 

 visible for many miles around. Though varying greatly in 

 character, the Itabira formation is in general hard and resist- 

 ant and much more durable than the softer schists which lie 

 immediately above and below it. The result is that wherever 

 the iron formation now appears at the surface in inclined beds, 

 it stands up in prominent ridges or as a chain of ''iron hills." 

 In some places where both the iron formation and the underlying 

 Batatal schist are very thin, the former may occur simply as a 

 capping, or cover sheet, following the contour of ridges of Caraga 

 quartzite. Elsewhere the iron formation constitutes a separate 

 range of hills in front of, and parallel to, the quartzite ridge. The 

 hills of iron formation are as a rule lower and less massive than 

 those of quartzite, though locally, as along the western rim of the 

 upper Santa Barbara valley, where the quartzite is relatively soft 

 and contains a good proportion of schistose layers, the iron hills 

 overtop the quartzites. 



The iron formation varies greatly in thickness. In the ridge 

 running east from Morro Agudo near Villa Rio Piracicaba, the whole 



^ C. K. Leith and E. C. Harder, "The Hematite Ores of Brazil and a Comparison 

 with the Hematite Ores of Lake Superior," Econ. GeoL, VI (1911), 670-86; E. C. 

 Harder, "The 'Itabirite' Iron Ores of Brazil," ibid., IX (1914), loi-ii. 



