NOTES AND QUERIES. 
165 
" giirgulho," which presents different characters in the Serviyo do Campo, and 
Servifo da Serra. In the former it is the product of itacolumite, formed of 
pure 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" (forma5ao), 
and their presence in the gurgulho is considered as a sign that diamonds are 
not far off. 
But on the Gui-guhlo 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 jnentioned as constituting the formation in the itacolumite 
we have included ratile and oxide of iron ; black tourmaline also, perhaps, 
should be mentioned, but no one has met with it. 
As the minerals associated \vith the diamond are found in the itacolumite, it 
is natui-al 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 Gurgulho do Campo is so called because it occurs in the plains and table- 
lands ; it is formed by the decomposition of metamorphic schist of wliich 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 quart zy, and allied 
according to M. Damour to schorl-rock. Thii-dly, hydrophosphate of allu- 
minum, hydroxyde of iron. Fourthly, hematite iron, red hematite, and 
perhaps titanic ii'on. 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 the itacolumite. 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 tliennderlymg 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 thrown into 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 "baiTo" occur also 
