374 E. C. HARDER AND R. T. CHAMBERLIN 



the high-level canga plain in the locality known as Gandarella, 

 40 kilometers northwest of Ouro Preto. 



Canga (from Itapanhoacanga, a village in central Minas) is a 

 peculiar ferruginous conglomerate consisting chiefly of fragments of 

 iron formation cemented with a nearly pure iron-oxide cement. It 

 is formed by a surface disintegration of the iron formation which 

 consists largely in the removal of silica, and solution and redeposi- 

 tion of iron oxide. In some places the canga has been deposited 

 almost in situ, while elsewhere it has been transported for con- 

 siderable distances and deposited, either on areas of iron formation, 

 or on adjacent areas of other rocks. 



Such canga deposits have probably been forming ever since the 

 iron-formation beds were exposed to surface erosion, and are being 

 abundantly formed at the present time. As a consequence they 

 are found at many different elevations. A long period of quiescence, 

 like that in which the land was worn low following the pre-Devonian 

 deformation, was therefore probably accompanied by abundant 

 canga deposition which formed extensive canga plains on, and 

 adjacent to, the belts of iron formation. But subsequent erosion 

 has been so extensive that today few remnants of canga formed dur- 

 ing the great base-leveling period remain. 



The Gandarella canga plateau, already mentioned, is the most 

 conspicuous of the high-level canga plains and is situated on the 

 summit of the divide separating the waters of the upper Santa 

 Barbara valley from those of the upper valley of the Rio das Velhas. 

 This canga plateau has an approximate elevation of 1,450 meters, 

 a little lower than the Serra do Caraga. Whether it is to be 

 regarded as a portion of the Caraga peneplain, now at a lower level 

 than the rest of the plain, and so more or less contemporaneous 

 with the Diamantina conglomerate, or whether it is to be taken as 

 the work of a later cycle of erosion, and to be correlated with 

 evidences of planation at a similar elevation in Alegria and near 

 Antonio Pereira, may perhaps best be left open for the present. 

 Deep valleys have been cut in this remnant of the canga plateau 

 along both sides of the divide. Along the bottom of one or two of 

 these at Gandarella, there occur irregular deposits of clay and sand 

 containing lignite and fossil leaves. On the basis of the plant 



