BRAZILIAN DIAMONDS AXD THEIR ORIGIN. 619 



identified. A comparison of them with other strata of the Sao Fran- 

 cisco Valley, which are characterized by the presence of palaeozoic 

 corals, permits me to affirm that they certainly ascend as far back as 

 the Silurian period. Other travelers, previously to myself, have men- 

 tioned this formation, and my friend the geologist Dorville-Derby, 

 who supports my view, has carefully described it. The washing of 

 these clays is performed in the same manner as that of the gravels, 

 and I have myself extracted diamonds from them. In the washing, 

 the minerals which we found rolled and rounded in the river-sands, 

 and presenting an entirely different aspect, came out in perfect crys- 

 tals, without a trace of wearing. They are the same satellites of the 

 diamond, but still in their primitive bed. The diamonds also of Sao 

 Joao da Chapada are characteristic : like the crystals of oxide of 

 iron, their angles are whole ; their wrinkled faces and their uniform 

 color have suffered no modification by friction. Should not the same 

 conclusion be adopted for the diamond, and may we not assume that it 

 also is here found where it was formed ? It is true that I have not 

 found diamonds actually in the little veins of quartz that traverse these 

 beds, nor in the schists, the decomposition of which has produced the 

 diamond-bearing clays with these same crystals of oligist iron and 

 rutile. But hardly one diamond exists to a million crystals of oligist 

 iron ; more than thirty thousand pounds of clay have furnished only 

 ten little diamonds weighing about a carat. It would have been a 

 rare chance to perceive, even with a strong glass, one of these stones, 

 no larger than the head of a pin, in the midst of an enormous mass of 

 sterile substances. Objections may indeed be made to the views which 

 I have presented. The formations in which the diamond is found 

 have not always been in the condition in which we now see them. 

 They are not eruptive rocks, that have come already formed from the 

 center of the earth, but have originated from the destruction of more 

 ancient formations, and have undergone metamorphic action under 

 the influence of which new crystalline elements have been formed 

 within them, and they have assumed the aspect they now present. 

 Why, it may be asked, may not the diamond also have been derived 

 from these primitive formations ? And then the problem, instead of 

 having been resolved, is. only put back another step. 



I may reply to this by asking if the processes of trituration effect- 

 ive enough to reduce crystals of feldspar and quartz to mud and sand 

 would not also have modified the diamonds by smoothing their angles 

 and we'aring away their surface ; especially, since we have seen that 

 much lighter rubbings have been enough to produce such effects in 

 the streams ? I could likewise answer other objections that my mind 

 suggests ; and I believe I have shown that the diamond of the allu- 

 vial formations of Diamantina comes, like the iron and titanic oxides, 

 the tourmalines and the phosphates, its faithful companions, from the 

 destruction of the quartz-veins intercalated into the palaeozoic rocks of 



