390 



J. C. Eninner — lite Scvra <h Jacobina. 



The foUowinji; tlioories have been entertained in an attempted 

 explanation of tlie tacts thus far o-athered in regard to the 

 Serra de .laeobina: 



I. The theory of a single synclinal fold having the two 

 eastern members turned back so far that the beds have the 

 same dip as the western ones. The relations would then be 

 such as are suggested by the accompanying section. 



Fig. 5. 



Fig. 5. Theoretical section to show the surface repetition of beds in a 

 synclinal fold. 



If this were the cori-ect explanation of the structure of the 

 range one should expect to find the ridges B and //to show 

 such similarity in material and sequence of their beds as are 

 commonly found in sedimentary deposits at similar distances 

 from each other. The same would be true of ridges D and F 

 and of the valleys C and G. At £'one would expect to find 

 a double thickness of a single bed or group of beds. To put 

 it differently : starting at JE, the axis of the syncline, one 

 should find the same or nearly the same sequence of rocks in 

 passing from E to A as he would in passing from E to I. 



It cannot be said that the study of any of the sections exam- 

 ined across the range has been sufficiently critical to settle this 

 point beyond question. The facts that appear to bear upon it, 

 however, are mostly unfavorable to tlie theory of a synclinal 

 fold. These facts are here given very briefly. 



1. Along the eastern face of the I'ange is a series of manga- 

 niferous schists or shales that is repeated on its western side at 

 only one place, so far as seen, and that is at and north of the 

 village of Brejao. The distance through the range on this 

 theory, however, is large enough to diminish considerably the 

 importance of this particular fact. 



2. So far as is now known, the conglomerates of the western 

 ridge of the i-ange are not repeated in the eastern ridge. Plere 

 again the distance through the range may be urged against the 

 probability of the similarity of the beds over so wide a zone. 



