42 O. A. Derby — Occurrence of the Diamond in Brazil. 



minerals obtained by him in washing several tons of material 

 from the different layers were, besides the diamond, anatase, 

 rutile, specular iron, martite, and tourmaline. 



In the Diamantfna region, therefore, the diamond occurs in siiu 

 in its original matrix in more or less well-defined veins travers- 

 ing the hydromica schist and itacolumite formation. It occurs 

 also as a transported pebble in the upper quartzite formation. 

 In the superficial gravel beds of the highlands, it occurs in its 

 second or third place of deposit according as these have been 

 derived from the- wearing down of one or the other of the older 

 ■•earing series. In many places it is probable that 

 the superficial grav< Is ire of diamonds from 



both these series, and it is certain that this is the case in the 

 river gravels, which may also contain diamonds washed from 

 the superficial gravels and that are therefore in their fourth 

 place of deposit. 



If an observation made to me by Mr. Meziel F. de Aguiar, 

 owner of the Sopa mine, be exact, the diamond-bearing veins 

 -tent over long distances. He stated that a straight 

 line drawn from the Sao Joao mine through the Sopa and pro- 

 longed to the southward would pass through or near some half 

 dozen of the most noted campo washings. Such a line would 

 have a length of about twenty miles, ancl it corresponds exactly 

 with the general strike of the beds in this region. In fact I 

 noticed at the Sopa mine that the line of strike prolonged 

 would cut the deep excavation of Sao Joao which was plainly 

 visible at a distance of four or five miles, I have reason to sus- 

 pect, from the information given by this intelligent minor, that 

 the true barro formation occurs also at the Sopa, though it has 

 never been recognized as such. 



Near the river Sao Francisco there is a rich river washing 

 on the river Jequetahy, which flows over beds of series e of the 

 general section which here consist of conglomerates that have 

 probably furnished the diamonds. The same conditions are 

 repeated on the river Aba. etc on the opposite side of the valley. 

 The divide between thy Sao Francisco and Upper Parana val- 

 leys, which lias rich diamond washings <m each -lope, presents 

 a repetition of the geological features of the Serra do Kspinhuco, 

 and so far as can be learned the general geological structure of 

 the diamond fields of the provinces of Bahia, Goyaz, Matto 

 Grosso and Parana is substantially the same as that above 

 described for the central part of tin pi<»\ \\ e ..f Minas Geraes. 



