0. A. Derby — Occurrence of the Diamond in Brazil. .">!* 



localities are on opposite sides of a high rounded ridge forming 

 the divide between the Jequetinhonha and the Eio Pardo, an 

 affluent of the Eio das Velhas. This ridge is composed for 

 the most part of schists and quartzites of the lower series, with 

 occasional outliers of the upper series. At the Sopa mine a 

 deep excavation near the top of the ridge shows at the top a 

 layer of red soil with a thin bed of gravel beneath ; then a 

 thick layer of reddish sand with scattered pebbles which passes 

 into a coarse gravel containing pebbles of various kinds and 

 bowlders of quartzite and schists. The bottom of the excava- 

 tion is formed by decomposed schists and schistose quartzite in 

 highly inclined beds traversed by veins of lithom- 

 smoky quartz. These beds present an irregular surface which is 

 evened up by the sand and gravel deposit. 



There is a marked difference between the upper and lower 

 diamantiferous gravel beds of this place which though hard to 

 define has been recognized by the miners who give a special 

 name, Sopa (soup), to the lower gravel. I take the upper bed 

 to be the usual superficial and modern gravel deposit due to 

 sub-aerial denudation, and the lower one to be a decomposed 

 conglomerate, belonging to the upper quartzite series. At the 

 neighboring locality >\ Guinda the conglomerate character of 

 the deposit is even more apparent, and I am convinced thai 

 both of these deposits can with safety be referred to the same 

 category as those of Bom Successo and Boa Vista. 



About 100 miles to the northward of Diamantina on a stream 

 called Corrego dos Bois near the city of Grao Mogol, there is a 

 famous iocality where the diamond has been mined in a solid 

 rock which has always been classed as itacolumite. Neither 

 Claussen von Helmreichen, nor Heusser and Claraz, who visited 

 this locality, recognized the distinction between the upper and 

 lower quartzites, and their descriptions therefore leave one in 

 doubt as to which series the diamond-bearing rock should be 

 referred. The rock is described as a compact itacolumite en- 



The presence of these masses led von Helmreichen to con- 

 sider the view, which he ultimately rejected, that tins was a 



regenerated rock, that is, a conglomerate. I have elsewhere 

 (Archivos do Museu Nacional. vol. v), maintained the opinion 

 that these masses are true rolled pebbles, and that this rock 

 belongs to the upper quartzite series. 



The conglon i u character of the diamond - bearing rock 

 has now been clearly established by Professor Goreeix who 

 was so fortunate as to obtain at Diamantina a specimen show- 

 ing a rolled pebble of hyaline quartz alongside of an embedded 



