2G'2 Branner — Geology of the Ser?'a do JItdato. 



are sinijily tlie conspicuous spurs of an elevated region lying 

 to the south. From one position on the plain to the nortlieast 

 as one looks back toward this group of mountains their structural 

 relations to each other can be readily seen. The accompanying 

 profile was sketched from that point. 



A later trip made across the region south and west of this 

 group of mountains, and trips made by assistants along the Rio 

 Sao Francisco, show that the quartzite beds that cap the Serra 

 do Mulato in a similar way form the flat summits of the Serra 

 do Encaibro just east of Sentose, and of the Serra do Tomba- 

 dor south of Ilemanso. In other words, the great group of 

 mountains sometimes spoken of as the Serras do Sao Fran- 



FiG. 6. > 



Fig. 6. Diagrammatic section showing the structural relations of the 

 Serra da Crnz, Serra do Boqueirao, and Serra do Miilato. The crests are of 

 Tombador quartzites ; the slopes aud plain are of old crystalline rocks. 



cisco have these quartzites at the base of a great sedimentary 

 series that is developed in the diamond regions of the interior 

 of Bahia. 



It remains to call attention to the relations of the Serra da 

 Batateira to the Serra do Mulato and the other mountains in 

 the latter cluster. That particular range is mentioned here 

 because it represents a type of geologic structure common at 

 many places in the state of Bahia. It seems clear that the 

 Serra da Batateira belongs to a series of very old sediments 

 that have been closely folded and faulted. Whether these 

 sediments are older or newer than the crystalline rocks next to 

 them is not certainly known at present, but the writer is of the 

 opinion that most of the granites are older. The structure, in 

 so far as it was made out in two trips across the region, is 

 shown by the accompanying section. (See fig. 3. 



In the i-egion south of Joazeiro and east aud south of Villa 

 Nova are similar narrow, sharp, quartzite ridges with their beds 

 standing nearly on end. These ridges generally have the gran- 

 ites and gneisses on both sides of them. This leads one to con- 

 clude that they are the last remnants of a very old series of sed- 

 iments let down into the older granites by faults, perhaps as 

 suggested in the accompanying section. (Fig. 7.) 



Tlie limestones in the section are recent, possibly Tertiary, 

 fresh-water deposits surrounding the ridge, and have been cut 

 out, or were never deposited, along the stream courses. The 



