346 E. C. HARDER AND R. T. CHAM BERLIN 



Somewhat more limited in occurrence is the iron formation which 

 is well developed in the broad portion of the area between Ouro 

 Preto and Bello Horizonte, but which to the northeast and south- 

 west becomes inconspicuous or is entirely absent. The upper 

 formations are also local in their occurrence (Fig. 2). 



The Caras:a quartzite forms the most prominent mountain 

 system of this portion of Brazil which has taken the name Serra 

 do Espinhafo, or Backbone Range, and which divides the waters 

 flowing westward into Rio Sao Francisco from those flowing east- 

 ward directly into the Atlantic Ocean. The iron formation gener- 

 ally forms well-marked foothills along the quartzite ridges, though 

 locally, where well developed, and specially hard, it itself forms 

 the main ridges while the quartzite is on the slopes. The Piracicaba 

 schist, being soft, is inconspicuous topographically, but the Itacolumi 

 quartzite forms a number of prominent peaks and ridges. 



The distribution of formations is well shown by the topography. 

 The mountain peaks and long continuous ridges common to this 

 region are made up of quartzite and iron formation. They are 

 bounded by lower areas of schist, or by an irregular undulating 

 region of hills and valleys underlain by gneiss and granite. These 

 sedimentary rock mountains of central Minas Geraes are, with 

 the exception of the granite masses forming the Itatiaya Range 

 on the southern border of the state and Caparao Mountain on the 

 boundary between Minas Geraes and Espirito Santo, the most 

 conspicuous mountains in Brazil. 



The characteristic deformation of the rocks of central Minas 

 Geraes has been thrust faulting and accompanying folding. The 

 forces in general came from the east and south, ranging between 

 northeast, southeast, and south, forces from different directions 

 being applied at difl'erent times, resulting in a sort of superimposi- 

 tion of structure. This complex structure is especially character- 

 istic of the wide area between Ouro Preto and Bello Horizonte, 

 where the combination of forces has resulted in the formation of a 

 number of parallel and intersecting belts of sedimentary rock. In 

 the southern part of this area is an east-west syncline resulting in 

 two parallel belts of sediments; in the western part is a north-south 

 overturned syncline causing a similar distribution, and in the 



