38G 



J. C. Bnxnner — The Serra de Jacobina. 



is one called the Serra de Sant'Anna, ten kilometers north of 

 the city of Bomiiui, This peak lias an altitude of 1100 meters 

 above tide level (tliree aneroid measurements). There are 

 considerably higher points in the range farthei south in the 

 vicinity of Saude, Jacobina, and Canna Brava. 



Sections across the Serra de Jacobina made at different 

 places differ but little from each otlier. Everywhere the rocks 

 are conglomerates, quartzites, and talcose shales or schists w^ith 

 steep dips toward the east. Along the western base of the 

 range these sedimentary beds rest upon granites or old erup- 

 tives, while on the east side also the granites and other crys- 

 talline rocks come close up to its base. The city of Jacobina 

 stands at the western base of the Serra de Jacobina where that 

 range is cut in two by the liio Itapicurii. Near that city on 

 the west side of the range the granites and old crystalline rocks 

 extend westward from the foothills of the Serra de Jacobina 

 to and up the slope of the Tombador range. It should be 

 clearly understood that the Serra de Jacobina is entirely dis- 



FlG. 1. 



Fig. 1. Section along Eio Itapiciiru at Jacobina where it cuts through 

 the Serra de Jacobina. 



tinct from the Serra do Tombador, which is a parallel range 

 some thirty kilometers west of Jacobina. The Jacobina range 

 is formed of sedimentary beds, mostly quartzites, alternating 

 with slates or schists, standing nearly on end, and is high, nar- 

 row, rugged and picturesque. The Tombador range is low, of 

 even horizontal crest, made of nearly horizontal sandstones and 

 quartzites that rest upon granites and form a vertical escarp- 

 ment along the east face of the mountain, while on the west 

 they dip gently westward and pass beneath the Salitre valley. 

 The diagram given at page 337 of the article on the Serra do 

 Tombadorf shows the relations of these two mountain ranges 

 to each other both topographically and geologically. 



The sections examined across the Serra de Jacobina are here 

 given in more detail. 



The city of Jacobina is at the parting between the granite 

 area west of the Serra de Jacobina and the quartzites that 

 form the serra itself. The actual contact between the two 

 kinds of rocks is not exposed on Rio Itapicurii in the town. It 

 is quite evident, howevei-, that this contact crosses the middle 



f This Journal, vol. xxx, p. 335. 



