GEOLOGY OF CENTRAL MINAS GERAES, BRAZIL 345 



stratigraphic position and lithology and their similarity to Algon- 

 kian sediments in other places. They lie upon the eroded surface 

 of the basement complex, and have as their basal member a great 

 quartzite formation. Above this quartzite, often separated from 

 it by a thin argillaceous schist bed, is the peculiar iron-bearing 

 quartzite known as itabirite, accompanying which are extensive iron- 

 ore lenses. This formation is, in turn, overlain by a schist and 

 quartzite formation of great thickness. The uppermost known 

 member of the great series is a quartzite with associated schists. 

 Occurring in proximity to these metamorphosed sediments, and 

 derived from them by disintegration and decomposition, are 

 subaerial deposits of more recent age. 



Appropriate geological names taken from localities where 

 characteristic exposures of the various formations occur have 

 been adopted. The known succession is as follows: 



Tertiary and Quaternary- 

 River gravels 



Tertiary clay and lignite 



Canga deposits 

 Mesozoic or Early Tertiary 



Diamantina conglomerate 

 Probable Algonkian 



Itacolumi quartzite 



Piracicaba schist and quartzite 



Itabira iron formation 



Batatal schist 



Caraga quartzite 

 Probable Archean 



Gneiss, granite, and schist 



The various sedimentary formations are complexly distributed, 

 occurring in some places and being absent elsewhere. Their 

 irregularity of occurrence is due, in part, to irregularity in original 

 deposition, but more especially to later faulting and folding followed 

 by very extensive erosion. They are separated from the basement 

 complex by a profound unconformity. 



The most characteristic formation of the series is the Caraga 

 quartzite which extends throughout the length and width of the 

 sedimentary area and locally develops an extraordinary thickness. 



