2 GO Brannei" — Geology of the SeiTa do Mulato. 



the slopes are covered witli a dense growth of catinga forest 

 and cactus difficult to penetrate even under the most favorable 

 circumstances. 



On the mountain slope at an altitude of 450 meters the 

 ground in certain localities is strewn with enormous quantities 

 of large, loose, somewhat waterworn bowlders. These bowl- 

 ders are mostl}- of the sandstones and quartzites that form the 

 resisting ledge that caps the summit of the mountain. This 

 belt of bowlders suggests the possibility of an ancient water 



Fig. 4. 



Fig. 4. Serra do Mulato seen from fazenda Itumerim. The flat summit 

 is of Tombador quartzites ; the slopes and plain in the foreground are of 

 crystalline rocks. 



level. It is here mentioned because at about the same altitude 

 similar bowlder zones have been found at other places in the 

 valley of the Rio Sao Francisco. At 580 meters is an exposure 

 of soapstone or talc that forms a belt running along the north- 

 eastern side of the Serra do Mulato. At 640 meters fragments 

 of dark hornblende schists are strewn over the surface of the 

 mountain slope. At YOO meters the rocks are compact black 

 ei-uptives resembling diabase. At 740 meters is the base of 

 the vertical escarpment made by the massive quartzites that 

 form the flat top of the mountain. 



In order to pass the wall made by these quartzites and reach 

 the summit of the mountain it was necessary to skirt along 

 the east base for about two kilometers. Nowhere in this dis- 

 tance was the actual contact between the quartzites and the 

 underlying crystalline rocks seen; it is evident therefore that 

 the contact is lower down the mountain slope and is concealed 

 by talus and soil. 



The necessity for skirting the base of the bluffs afforded an 

 excellent opportunity for examining the rocks and looking for 

 fossils. The quartzites are mostly fine-grained, and nearly all 

 of them show false bedding with remarkable clearness. In 

 the talus slopes below were seen abundant angular blocks of 

 conglomerate, which must necessarily have come from some 



