368 



E. C. HARDER AND R. T. CHAMBERLIN 



The rocks did not everywhere yield to the stresses in the same 

 way. In the southeastern part of the district the strata were 

 thrown into open folds, though these folds show less symmetry 

 than those of the Jura or the Appalachian system. With the 

 folding there is also some faulting associated. But in the north- 

 eastern portion of the district very little folding has occurred. 

 That region has suffered, instead, very extensive thrust faulting 

 which repeats the sedimentary series, and by thus repeating the 

 outcrops of iron formation becomes a factor of much economic 

 importance. The fractures have occurred along lines trending for 

 the most part northeast and southwest, or parallel to the Atlantic 

 coast. The faults are overthrusts from the southeast and east. 



3000' 



Ckxraoa 

 QuarJzile 



Cta7?ife and GneJ33 CaraQo. J^raa'caba 

 QuarJzJte i5cMj] 



Crani/e and Gnebs 

 Fig. 7. — Slice-faulted section between Villa Rio Piracicaba and Morro do Seahara 



The type of faulting can perhaps best be described as slice 

 faulting (Fig. 7). The strata, instead of yielding to the stresses by 

 wrinkling and folding, were sliced off in a succession of inclined 

 blocks nearly all dipping toward the east or southeast, and the 

 crustal shortening accomplished by movements between the inclined 

 slices. In the northern portion of the Minas Geraes iron-ore dis- 

 trict, the slice faulting has caused an alternation of the crystalline 

 complex with the sedimentary series. Nearly everywhere the 

 basement complex is the surface formation on the up thrust side. 

 On account of the great erosion which the region has suffered since 

 the period of deformation, the sedimentary formations have 

 persisted only on the downthrown side of each fault. In the 

 western part of the district also, faulting would seem to dominate 

 folding. 



