ON THE GENESIS OF THE DIAMOND 1 23 



wear of transportation that have contributed to the deposit, 

 together with the isolated minerals derived from the breaking 

 down of these rocks and of such others as have entirely disap- 

 peared as rock-masses and are now only represented by the more 

 resistant of their constituents, which have been more or less 

 completely assorted according to their resistance to disintegra- 

 tion and to wear, to their specific gravity and to the size of 

 grain. These isolated minerals, the formation of the miners, who 

 attach great importance to them, can in some cases, as of zircon, 

 monazite, xenotime, etc., be referred with tolerable certainty to 

 original eruptive rocks, though they may, and in many cases 

 doubtless have, passed through others before reaching their 

 present place in the gravels ; others, as staurolite, disthene, etc., 

 can with equal certainty be referred to metamorphosed elastics, 

 but by far the greater part, as quartz, the iron and titanium 

 oxides, tourmaline, garnet, and many others might be from either 

 eruptives or metamorphosed elastics, or from both. The min- 

 erals which can with more or less probability be attributed to erup- 

 tive rocks, are not so predominant or so constant in their occur- 

 rence that any particular significance can be attached to them. 

 Their evidence, so far as it goes, points rather to the acid 

 eruptives, as granites, etc., than to the ultra basic types of the 

 Kimberley district. 



In only one Brazilian mine, so far as known, are basic eruptives 

 a characteristic feature, and in this the conditions are such that 

 the association seems to be accidental rather than genetic. This 

 is the Agua Suja (dirty water) mine in the Bagagem district of 

 western Minas Geraes, which has been excellently studied by 

 Messrs. Gonzaga de Campos, Hussak, and Calogeras, 1 though 



from the gold mine of Antonio Pereira, near Ouro Preto, which is the only known 

 Brazilian locality of scorodite, but is not known as a diamond locality. The specimen 

 is reported to come from the Abaiete district to the west of the Sao Francisco, but no 

 other specimens of scorodite, or of limonite of this character, are known from that 

 region, where, moreover, only gravel deposits had been worked, whereas the speci- 

 men in question is evidently from a mine, and not from a deposit of transported mate- 

 rial. 



1 Gonzaga de Campos: Jazidas Diamantiferas de Agua Suja, Rio de Janeiro, 



