J. C. Branner — The Serra de Jacohina. 



391 



II. The second tlieory is that of the repetition of tlie same 

 beds by four parallel faults. This theory would require but 

 one series of quartzite beds and an overlying series of schists 

 or slates. Four parallel faults, as suggested in the accompany- 

 ing figure, might yield the general structure of the range. 



Fig. 6. 



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Fia. 6. Ideal section across the Serra de Jacobina on the theory of its 

 having been formed by four parallel faults. 



The chief objection to this theory is the great length of the 

 range and its apparently uniform character throughout. It 

 would be very remarkable to find four faults so evenly spaced 

 for 225 kilometers and following each other in the curves 

 made by the range throughout that entire distance. 



A second objection is that the manganiferous shales or slates 

 near Villa Nova and Jaguarary are not repeated in the valleys 

 within the range as we should expect if the structure were pro- 

 duced by such a series of faults. Similarly the heavy con- 



FiG. 7. 



Fig. 7. Section across the Jacobina range on the theory of a single fault 

 ■with the downthrow on the west. 



glomerates at the base of the series at Jacobina are not repeated 

 in the easternmost ridge of the range. 



