380 ORVILLE A. DERBY 



knobs and ridges. '5_,The soil cap is generally thin, gneiss and granite 

 rocks appearing underneath it. With these occur considerable 

 stretches of a black schistose rock, which is presumed to be mica or 

 hornblende schist. A considerable part of this section of the road 

 is along the watershed between the Paraguassii and Itapicuru, de- 

 scending afterward to the valley of the latter. To the westward of 

 this comparatively level section rises (kil. 257; alt. 343™) the Serra de 

 Itiuba, a bold ridge of red granite estimated to be about 800"^ high. 

 The road crosses it in a gap at an elevation of 437™, and descends 

 to the river Itapicuru (kil. 280) at 354™, and then ascends over gneiss 

 and granite to the city of Bom Fim (kil. 320), on the flank of the 

 Serra do Espinhafo, at an elevation of 548"^. On the ascent to the 

 summit (kil. 355; alt. 683"^) the cuttings are in granite to kil. 333, 

 where flaggy quartzites begin to appear and continue, with occasional 

 interruptions of granite, to Angicos station (kil. 383; alt. 487"^), which 

 is a little beyond the western base of the serra. From Angicos to the 

 end of the line at Joazeiro (kil. 450; alt. 372™) the country is a gradu- 

 ally sloping plain, so slightly accidented that for 60 kilometers the 

 road has been laid out on a perfectly straight line. Scattered knobs 

 and ridges of granite, gneiss, and quartzite rise abruptly above the 

 general uniform level. The rocks seen from the foot of the Serra 

 do Espinhafo to kil. 391 (alt. 490"^) are gneiss and granite, with 

 occasional outcrops of quartzite. From this point to kil. 430 (alt. 

 416"^) the surface rock is a whitish limestone in horizontal beds, and 

 of only a few meters' thickness. The aspect of the rock is that of 

 a fresh-water deposit, and though no fossils could be found, it is 

 presumed to be of Tertiary, or possibly Quaternary, age. A similar 

 limestone is known to occur higher up the river in the neighborhood 

 of Chique-Chique, where it appears to cover a considerable area. 

 Along the last 20 kilometers of the road gneiss and granite reappear. 

 A recent excursion to the diamond region of the upper Paraguassu 

 basin gave me an opportunity to examine the section characteristic 

 of the valley of that river. The trip was made by the Bahia Central 

 Railroad to its terminal station, Bandeira de Mello, situated about 

 100 kilometers, by the river, to the east of the point where it escapes 

 from the serra at Passagem (see annexed sketch map), the remainder 

 being made on mule-back. The railroad, starting from Sao Felix 



