40 0. A. Derby — Occurrence of the Diamond in Brazil. 



diamond (Comptes Rendus, No. 25, 1881). Professor Gorceix 

 considers, however, that this rock may possibly belong to the 

 lower .series since conglomerates with pebbles of hyaline quartz 

 have recently been discovered in that series as well. In von 

 ben's complete memoir, which I have only recently 

 seen, there is a sketch of the locality which shows conclusively 

 that both quartzites occur at the Corrego dos Bois, and that the 

 diamonds are found in the upper one just above the line of 

 junction of the two series. This sketch is interesting also as 

 showing how close must be the resemblance of the two rocks 

 to have led so able a geologist (as. von Eschwege also, in other 

 places) to overlook such unmistakable evidence of the exist- 

 ence of two unconformable series. 



In the four localities of Bom Successo, Guinda, Sopa and 

 Grao Mogol the diamond occurs with rolled pebbles derived 

 from older rocks and must itself be regarded as a pebble in its 



in gravel deposits that ure clearly of modern origin. The 

 facts above presented proving the existence in this region of a 

 conglomerate formation or of a quartzite containing scattered 

 pebbles which has suffered extensive denudation, will explain 

 the origin of these deposits without recourse to theories of 

 glaciation or of former systems of drainage different from the 

 present ones. I may mention here by way of parenthesis that 

 in many other parts of Brazil, where anomalous gravel deposits 

 occur that in northern latitudes would be set down without 

 as of glacial origin, I have recognized the presence 

 of pebble-bearing formations. In other washings the gravel 

 consists of angular fragments of vein quartz left on the surface 

 by the wearing down of the soft beds traversed by the veins. 

 In these cases the matrix of the diamond must be near at hand, 

 but so far as I am aware it has never been sought for. 



By far the most interesting of the servicos do campo is that of 

 Sao -l >& • ' -r.iue twelve miles to the west of 



Diamantina on a high rounded ridge lying between the Caethe- 

 miritn. a famous affluent of the Jequetinhonha, and a stream 

 flowing to the Rio das Yelhas. The singular feature of this 

 mine is the occurrence of the diamond in clay or earth (barro). 

 ft has been examined and described bv Ileusser and Clairtz. 

 vonTschudi and Burton, but its true character was first pointed 

 out by myself (Archive do Muscu .Vaca„ial, vol. v, 1881), and 

 by Gorceix (Comptes Rendus, No. 25, 1881). 



Two mines, the Barro (clay) and the Duro (hard), opened on 

 opposite sides of the ridge, have been worked until they met 

 at the center producing an excavation several hundred meters 

 long and some twenty or more meters deep which closely 

 resembles a railroad cutting the sloping sides of this cut show 



