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



Itacolumite as a formation name has been used, not only for 

 the quartzite above the iron formation (the quartzite out of which 

 the peak of Itacolumi has been carved), but also for the great 

 quartzite series (Caraga quartzite) which, throughout the district, 

 underlies the iron formation. That the quartzite which makes up 

 the peak of Itacolumi is distinct from the tremendous quartzite 

 formation of the Serra do Caraga is a fact which does not seem to 

 have been brought out clearly by those who have studied this 

 region; nor has it been clearly recognized that the quartzite which 

 forms such a large part of the Serra do Espinhago from Ouro Preto 

 northward to Diamantina is the lower. But these two quartzite 

 formations are quite distinct and are separated from one another 

 by the Itabira iron formation and two schist series. If the name of 

 Itacolumi be applied to one of the quartzite formations, it would 

 seem fitting that it should be applied to that one which occurs in the 

 peak of Itacolumi. This is the upper quartzite. 



In areal extent the Itacolumi quartzite is much more limited 

 than the Caraga quartzite. This is chiefly the result of erosion 

 which has swept away the upper members of the Minas series from 

 many localities where the lower members still remain. The Ita- 

 columi formation is nowhere better displayed than just south of the 

 city of Ouro Preto in the mountain ridge which culminates in the 

 peak of Itacolumi, where there are perhaps 1,200-1,500 meters of 

 quartzite exposed. The upper quartzite appears again on the 

 north limb of the Ouro Preto anticline, as a conspicuous ridge 

 just north of the village of Bento Rodrigues. 



Whether the Itacolumi quartzite was once overlain by younger 

 sediments of the same general series, or not, is uncertain. As yet, 

 no evidence of a younger member of the series has been recognized. 

 But as the Itacolumi quartzite, though a resistant formation, 

 remains only at a few points in the whole district, it is not impossible 

 that younger, and less resistant, beds may once have capped it and 

 since been removed by erosion. 



Summary. — This whole great series of sedimentary formations 

 is apparently conformable throughout. Above the base of the 

 Caraga quartzite no unconformity of any moment has been noted. 

 But from top to bottom, not a single fossil has been found within 



