SERRA DO ESPINHAQO, BRAZIL 375 



the adjacent zones, particularly the one lying to the eastward. The 

 tectonic features of the range have, on the contrary, scarcely been 

 touched upon by him or his successors. 



Owing to its wealth of gold and diamonds, the southern section 

 of the range, from Ouro Preto to Diamantina, has been frequently 

 visited and described, with attempts to give an idea of its geological 

 characteristics; but, with the exception of the writings of Eschwege, 

 Spix and Martius (3), Helmreichen (4), Henwood (5), and Hussak 

 (19), but little is to be found in the somewhat voluminous (as com- 

 pared with other parts of Brazil) literature relating to this region that, 

 from a geological point of view, is comprehensible, or, being so, is 

 of permanent value. The remaining sections and the regions on 

 either side are almost a terra incognita horn, both a topographic and 

 a geologic point of view, and, as in all other parts of Brazil, the lack 

 of reliable maps is an almost insuperable obstacle to detailed geologic 

 studies. The present sketch is based on a few flying trips to the 

 above-mentioned gold and diamond regions, a hurried and partial 

 examination of the diamond-bearing section in the state of Bahia, 

 a boat trip on the river Sao Francisco and its tributary, the Rio das 

 Velhas, and an excursion into the region of the middle Jequitinhonha, 

 which, however, did not extend as far as the eastern margin of the 

 Serra do Espinhafo region. The observations that could be made 

 on these hurried trips, supplemented by the meager gleanings to be 

 found in the literature relating to the region, are manifestly inade- 

 quate for more than the most general treatment of the subject. 



The Serra do 'Espinhafo, as now understood, constitutes a zone 

 with a width of about 50 to 100 kilometers, and a mean elevation 

 of over 1,000™, characterized by rugged topographic features, and 

 rising with abrupt margins a few hundred meters above the lower 

 regions of more uniform topography on either side. It extends in 



in his time were known as the primitive rocks, among which he included, as a second 

 division, the bedded arenaceous ^nd argillaceous rocks of the Serra do Espinhago. 

 He did not admit a succession o' diments among them; he did not attempt to sub- 

 divide them into series. The n ;t unfortunate result of this point of view was the 

 lumping-together of all the qur ,^ose rocks of the region under the general name of 

 "itacolumite," which has bee.i- '. . incubus on Brazilian geological studies. Being 

 an acute geological observer, he did not fail to note evidences of the existence of 

 two unconformable series of beds among the rocks so classed, but, withheld by his 

 theory, he did not give these observations their due importance. 



