J. C. Branner — The ISerra de Jaodbina. 



389 



those found in tlie other sections. The schists are also exposed 

 on the phxin between the easternmost quartzite rid^e and the 

 town of Jaguarary. Througliout the whole section the rocks 

 dip eastward ; one dip measured in the purplish quartzites of 

 the eastei-n range was due east at an angle of sixty degrees. 



West of the range the rocks of the plain are granites and 

 gneisses and these rise more than half way up the western 



Fig. 4. 



Fig. 4. Section across the Serra de Jacobina between Jaguarar^ and 

 Piabas. Length of the section, ten kilometers. 



slope of the mountain. The actual contact between the sedi- 

 mentary series and the crystalline series was not seen ; those 

 observed nearest the quartzites are soft cream-colored rocks 

 that have the appearance of being composed of decomposed 

 feldspars. Below these are laminated gneisses in an advanced 

 stage of disintegration. 



At my request Mr. Koderic Crandall made a trip across the 

 serra along the upper portion of the Rio do Pogo Comprido, 

 which cuts across the Jacobina range twenty kilometers north 

 of Jaguarary. Mr. Crandall found the range at that place to 

 bo made up of four parallel ridges of quartzite whose beds 

 dip north eighty degrees east at an angle of seventy degrees. 

 Granites form the plains both on the east and the west sides of 

 the serra. The structure is, therefore, the same as that shown 

 in the other section across the range. 



The examples given are enough to show the remarkably 

 uniform structure throughout of the Jacobina range. They 

 also show at all the points examined the granites, gneisses or 

 other old crystalline I'ocks on both sides of the range. The 

 relations of the granites on the west side of the range to the 

 sedimentary series seems to be fairly clear : the form, conti- 

 nuity, and position of the parting suggest, if they do not posi- 

 tively prove, that the sedimentary series was laid down upon 

 the granites. On the east side of the range, however, the 

 contact between the granites and the sediments has not cer- 

 tainly been observed, and there is, therefore, more or less 

 doubt about the relations of the sediments of the serra to the 

 crystalline rocks of the plains to the east. Everywhere the 

 four main ridges of the serra are of extremely hard quartzites, 

 while the valleys are cut in soft talcose schists. 



