390 ORVILLE A. DERBY 



Some interesting information regarding the topographic and geologic 

 features of this route can be gathered from the narrative of Spix and 

 Martius (3), and from the report of Dr. Theodoro Sampaio (22). 

 The road, starting from Sao Fehx, is for some distance nearly coin- 

 cident with the railroad line above described, and over a gneiss .plain 

 of moderate elevation. It then rises to the top of a higher gneiss 

 and granite plateau at Maracas, at an elevation of about 1,000"^, 

 that occupies the watershed between the rivers Paraguassii and Rio 

 de Contas. This plateau, according to Dr. Sampaio, breaks down 

 to the westward in a wall-like face about 350"^ high which overlooks 

 an undulating region with detached hills that intervenes between it 

 and the Serra do Sincora, the eastern front of the Serra do Espinha^o 

 plateau. This region is also composed mainly of gneiss and granite, 

 but about the headwaters of the Rio Una a zone of reddish shale 

 and ash-colored limestone intervenes between the crystalline rocks 

 and the sandstone and conglomerate of the Serra do Sincora. The 

 Serra do Espinhafo section of the road, extending from the south 

 end of the Serra do Sincora to beyond Caetite, is mainly over a highly 

 inclined series of quartzites and argillaceous schists, which Spix and 

 Martius identified with those of the gold districts in Minas Geraes 

 (this region is also auriferous), with occasional exposures of gneiss, 

 micaschist, and granite. To the right of the road, and forming the 

 highest points of the region, these older rocks are overlain by a con- 

 glomeritic sandstone, which Spix and Martius referred to the Roth- 

 todtliegende, and which evidently represent spurs and outliers of 

 the sandstone sheet of the adjacent upper Paraguassu basin. The 

 western face of the plateau, known by the local name of "Serra 

 Geral, " is abrupt, but of no great altitude (850"^) at the watershed 

 near Caetite, where it is composed of gneiss. To the west of the 

 mountain front the road is over a nearly level plain of truncated 

 granite, gneiss, quartzite, and limestone rocks, but with isolated 

 knobs and ridges rising above the general level. 



To the south of the Rio de Contas road to Grao Mogol, in the 

 state of Minas Geraes, a distance of about 300 kilometers, but little 

 is known of the Serra do Espinhafo plateau beyond the fact that 

 diamonds occur in several localities. For the section about the 

 northern headwaters of the Jequetinhonha in the neighborhood of 



