34 O. A. Derby — Occurrence of the 



The diamond washings of the vicinity of the city of Dia- 

 mantina, in the province of Minas Geraes, afford examples of 

 several modes of occurrence of the diamond, which, so far as 

 known at present, may be taken as types of all the washings 

 of the empire. 



The diamond region of Diamantina is situated along the 

 crest and on both flanks of the Serra do Espinhaco, the great 

 interior mountain range of Brazil which divides the waters of 

 the Sao Francisco from those of the Doce, JequetinhoDha ami 

 other rivers. The general height of the watershed in this 

 region is about thirteen hundred meters above the level of the 

 sea or about five hundred meters above the general level of the 

 elevated plains of the Sao Francisco valley, lying immediately 

 to the westward. The prolongation of this range to the north- 

 ward includes the diamond region of Grao Mogol in the prov- 

 ince of Minas Geraes and that of the so-called Cbapada Dia- 

 mantina in the neighboring province of Bahia. 



The general geological structure of this region is n 

 in the following section based on the observations made in three 

 journeys by different routes between the river Sao Francisco 

 and Jequetinhonha. 



formable to the series containing the itacoiuinites or lower 



confusion is easily explained by the fact that most travelers 

 have confined their observations to the eastern side of the 



ivatershed where, owing to the two quartzites having the same 



