Branner — Geology of the Serra do Mulato. 263 



Fig. 7. 



Fig. 7. Section showing the 

 theoretical relations of the ridges 

 of vertical qnartzites. 



evidence of the age of these limestones is conclusive, but can- 

 not be presented here. 



Conclusions. — The excursion to the Serra do Mulato made 

 it possible to determine the following facts regarding the 

 geology of the region south and southwest of Joazeiro: 



1. The low flat region forming 

 most of the high flood-plain of the 

 Rio S. Francisco is made up of 

 two series of rocks : — I, an older 

 series of crystalline schists, other 

 inetamorphics, and eruptives; and 

 II, a series of highly metamor- 

 phosed qnartzites and schists or 

 shales. 



2. Faults have let the old qnartz- 

 ites down into the crystalline rocks 

 here and there, and the upturned 

 edges of these beds form the white 

 walled mountains and hills that 

 are scattered far and wide over the 

 old base-leveled plain. Tlie Serra 



da Batateira belongs to this type. (See tig. 3.) 



3. The flat-topped mountains so common to the west and 

 southwest of Joazeiro, such as the Serra da Cruz, Serra do 

 Mulato, Serra do Encaibro, and the Serra do Tombador south 

 of Remanso, are formed by approximately horizontal beds of 

 Paleozoic qnartzites which rest directly upon the old crystalline 

 series. 



4. This series of quartzites was later traced up the Rio Sao 

 Francisco, southward across Rio Salitre at the falls, and farther 

 south to the region about Jacobina. It usually forms a bold 

 escarpment. 



5. On account of this series of quartzites forming the Tom- 

 bador range west of the city of Jacobina, it has been named 

 the Tombador series. 



6. No recognizable fossils have thus far been found in these 

 Tombador quartzites. They are called Paleozoic on account 

 of stratigraphic relations found in the region to the southwest. 



7. Limestones cover the higher portions of the elevated flood- 

 plain of the Rio Sao Francisco. 



8. These limestones are of fresh-water origin and of Tertiary 

 and later age. 



Stanford University, California. 



