J. C. Branner — The Serra de Jacohina. 387 



of the city just west of the Conceigao church, and close to the 

 city jaiL Nortli of the city this parting comes out clearly in 

 the vegetation. The bare qiiartzites are covered with a stunted 

 growth of hushes, while the vegetation on the granites is more 

 vigorous and abundant, and its color is of a brighter green. 

 Along this west flank of the range toward the north one sees 

 clearly the eastward dip of the sedimentary series forming the 

 serra and the strike which is always parallel with the range 

 itself. Immediately south of the Itapicuru near Jacohina the 

 sandstones and quartzites near the contact are so jointed that 

 one can hardly find a block a foot in diameter. 



The influence of the rocks on the vegetation is noticeable 

 south of the river. The " monte" or peak with the cross at its 

 summit is just south of the city and 150 meters above it. The 

 north end of this I'idge is of green-stained, flinty quartzite con- 

 glomerate. The pebbles of these conglomerates are often as 

 large as hen's eggs, and the metamorphism is so complete that 

 the outlines of the pebbles are often obscure. A kilometer or 

 so farther south along this same ridge pebbles 15 centimeters 

 long are common. The fracturing or jointing of some of these 

 conglomerates and quartzites is remarkable. Over some expo- 

 sures there are three sets of parallel joint-planes intersecting 

 each other with striking regulai-ity at angles of thirty degrees, 

 and breaking the beds into small angular blocks. Another 

 striking characteristic of these basal conglomerates is that the 

 well-worn pebbles of which they are composed are themselves 

 made of quartzitic sandstones. In other words, these conglom- 

 erates are not derived from the underlying granitic rocks, but 

 from an older series of sediments. Some sixty-five kilometers 

 farther north the Kio Itapicuru cuts through the range, but 

 this section was not examined by the writer. 



Something more than a hundred kilometers north of Jaco- 

 hina a good section of the Jacohina range is exjjosed near the 

 town of Campo Formoso, where it is again cut by a stream, 

 the Rio do Campo Formoso or da Agua Branca. At this 

 place the mountain range as a whole is made up of four paral- 

 lel quartzite ridges dipping eastward at a high angle. The 

 hard beds of the series are quartzites very much like the so- 

 called itacolumites of Minas Geraes, while the yielding beds 

 are talcose schists. The town of Campo Formoso at the moun- 

 tain's western base stands on gi-anites, and the waters that unite 

 at this place to form Rio do Campo Formoso flow almost exclu- 

 sively from the granite area that forms the rolling country 

 immediately west of the Serra«de Jacohina. The plains that 

 extend eastward and southeastward from the serra's eastern 

 base are also of granites, mica schists, and other crystalline 

 rocks, with here and there a quartzite ridge rising above the 



