NOTES AND QUERIES. 



165 



" gurgolho," which presents different characters in the Servipo do Campo, and 

 Servico da Serra. In the former it is the product of itacolumite, formed of 

 pnre quartz sand, fragments of itacolumite and quartz. It fills the cavities 

 resulting from the distraction of certain beds of itacolumite, which are called 

 by the Brazilians canaes corrumes. 



The method of washing is described by D'Eschwege, and with the diamond as 

 residua are obtained rutiles, oxide of iron and oxide of titanium. These minerals 

 which occur more or less with the diamond are named the "formation" (formacao), 

 and their presence in the gurgulho is considered as a sign that diamonds are 

 not far off. 



But on the Gurguhlo de Serra these minerals are to rare that it is impos- 

 sible to recognize them without a previous washing, and even in certain beds 

 they are almost entirely absent. 



Of three minerals mentioned as constituting the formation in the itacolumite 

 we have included rutile and oxide of iron ; black tourmaline also, perhaps, 

 should be mentioned, but no one has met with it. 



As the minerals associated with the diamond are found in the itacolumite, it 

 is natural to suppose that the diamond comes from the same source. The 

 presence of diamonds in rivers rising in mountains of itacolumite is another 

 evidence of this fact which Pohl and D'Eschwage had announced as probable, 

 and Helmreicher has placed beyond doubt ; for at the Serra Grao Mayor at 

 Corgo dos Bois has proved that diamonds can not only be obtained from the 

 washing of the gurgulho, but also from the fragments of a rock of itacolumite, 

 which mode is not followed up because the washing process is easier and cheaper. 



The Gurgidho do Campo is so called because it occurs in the plains and table- 

 lands ; it is formed by the decomposition of metamorphic schist of which the 

 products are more or less mixed with itacolumite. The washing of the Gur- 

 gulho do Campo gives — firstly, blackish-grey grains and cyanite. Secondly, 

 a bluish-black rock, sometimes ferruginous, sometimes quartzy, and allied 

 according to M. Damour to schorl-rock. Thirdly, hy diphosphate of allu- 

 minum, hydroxyde of iron. Fourthly, hematite iron, red hematite, and 

 perhaps titanic iron. All these substances are derived from the metamor- 

 phic schist. As to the quartz, rutile, amatase, sub-oxide of iron, they proceed 

 equally from that and t he itncolumite. The ensemble of the minerals associated 

 with the diamond is called the " formation ;" but here these are so abundant 

 that it is often easy to distinguish them without a preliminary washing. 



The Gurgulho do campo is met with on the surface, near the separation of the 

 two great basins of the San Erancisco, and of the Jequitnihouta, at Dattas, at 

 Quinda, and at San Joao do Barro. As it does not appear to have been deposited 

 by water one is forced to admit that it has been formed in situ by the decompo- 

 sition of the underlying rock, sometimes, however, it has been water-borne some 

 little distance. 



As long as diamonds were found in the Gurgulho of the surface, they were 

 not sought deeper ; but about the year 1850 at San Joao do Barro the under- 

 lying schistose-rock was by chance submitted to the washing-process, when it 

 was found to contain many diamonds. Erom this time a course of deep-mining 

 has been pursued with the best results. The rock is so soft that it can be 

 extracted by means of hoes : it is then thrownfcinto the " cradle" and washed. 



When the rock is examined in situ a schistose structure is perceived, which 

 however has entirely disappeared in the gurgulho ; the solid and heavy parti- 

 cles alone remaining. 



The schisty rock found underlying the gurgulho is called " barro." It is of 

 a very variable colour — white, reddish, dark grey or black. It is soft to the 

 touch, and sometimes sand is obliged to be added to it to enable it to undergo 

 the washing process. Between the gurgulho and this "barro" occur also 



