GEOLOGY OF CENTRAL MINAS GERAES, BRAZIL 369 



Some of these fault lines are apparently of great length. A 

 great fault forms the eastern front of the Serra do Espinhago, or 

 Backbone Ridge, at Cocaes and from there runs northward for 

 many miles. Then, as we go farther north, there appear in front 

 of it to the east successively new faults arranged en echelon. Each 

 of these, in turn, commences a new front range slightly to the east 

 of the previous range. The old ranges continue northward as 

 successive ridges behind the front. This system of faulted ranges 

 runs northward into the state of Bahia.^ The displacement along 

 the major fault planes cannot be determined, inasmuch as the 

 sedimentary formations have completely disappeared from the 

 up thrust side, so that the crystalline complex alone remains. It 

 is probably great. In the minor slice faults the displacement in 

 some cases is as low as 300 meters. In general the faulting in 

 central Minas Geraes shows a marked similarity to that 

 in the Appalachian region of the United States and that in the 

 Canadian Rockies of Alberta. 



These deformative movements were very general, apparently 

 involving most of the Atlantic border of Brazil south of Cape St. 

 Roque, and possibly also Uruguay and portions of the province pi 

 Buenos Aires in Argentina. The mountains formed at this time 

 would seem, in a way, to be the Atlantic counterpart of the Andean 

 ranges on the Pacific border. South America was squeezed from 

 the Atlantic first and from the Pacific later. 



How closely the period of deformation followed the sedimenta- 

 tion is as yet unknown. Minas Geraes affords little evidence, but 

 in several of the neighboring states, Matto Grosso, Sao Paulo, and 

 Parana, strata of Devonian age, but sHghtly disturbed, are found 

 resting unconformably upon the wrinkled strata which participated 

 in these orographic movements.^ The mountain-building move- 

 ments were therefore accomplished before the Devonian. That 

 the deformation did not immediately precede the Devonian is 

 evident from the amount of erosion suffered by the mountains 



' O. A. Derby, op. cit. 



^J. E. Branner, Geologia Elementar, pp. 230-31; O. A. Derby, "Geologia da 

 regiao diamantifera da Provincia do Parana, no Brazil," Archivos do Miiseti National 

 de Rio de Janeiro, III (1878), 89-96. 



