166 
THE GEOLOGIST. 
various approximations to an earthy mass, wliicli also contains diamonds, and 
which is designated " terra." The barro'^aud " terra" are so decomposed 
and softened'that the holes worked in the clay are filled in during the night. 
It is only in the dry season that the deep mines in the barro can be worked ; 
the washing is carried on, on the contrary, in the rainy season. 
The veined structure of the barro at once tells of its origin in the metamorphic 
schist, a fact confirmed by the foUo^ring remarks. The schists lie nearly north 
and south and dip towards the east at an angle of thirty degrees. Besides 
underneath the "barro" a bed of granular itacolumite is met with called 
" Pizarro," it is easy to prove that this bed is intercalated in the schists and 
that its direction and dip are the same. On the other hand concretions are 
formed in its neighbourhood, as is the case at the termination of the metamorphic 
schist. Finally, the residue of the washing of tlie barro and the gui-gulho do 
campo is exactly the same. We have, besides, examined the stony fragments 
wliich are found in the " barro," and have proved that they have been derived 
from the metamorphic schist in different stages of decomposition : some frag- 
ments were so unchanged that we could not for a moment doubt their origin. 
It is very true that diamonds have not yet been found in the metamorphic 
schist, but that is easily understood as it has been so little worked. At the 
time that the barro is worked it is very soft and fuU of water ; it hardens how- 
ever on exposure. The diamonds it contains do not detach themselves at firft, 
and in the washing we have been fortunate enough to obtain, at Diamantina, a 
specimen of barro which still contained a very large diamond : it also showed 
very clearly the origin of the rock. We have also seen a similar specimen 
belonging to Mr. T. Redington, who possesses diamond mines between San Joao 
and Diamantina. 
Although there are many workings of the gurgulho at San Joao, that in the 
barro since 1S55 has yielded richer and more regular products, and while we 
were there preparations were being made to open another. Xear Quinda there 
are many workings of the gui'gulho in which the underlying bed is also washed ; 
but this bed has not the veined structure of that at San Joao, and is much 
more sandy. In this neighbourhood there is a sandy itacolumite, which cannot 
contain many diamonds, as it is never washed. 
Observation has shown that the schists most rich in diamonds are strongly 
impregnated with oxide of iron, and that they have a grey or blackish colour. 
The Servifo do Rio comprises the searches made in the beds and on the banks 
of rivers. This mode of diamond hunting, more common than the other 
methods, is used to seek them when washed from their original situation. As 
it has been often described, we need not enlarge upon it ; we have observed it 
in more than thirty localities from Cidade de Serro in almost all the water- 
courses on the road to Grao Mayor, especially at Poso Alto, Dattas, Quinda, 
Diamantina, Simao Yiera. The principal workings of tliis nature occur 
on the Jequitinhonha. The rivers generally have their beds in the solid rock, 
in which, in some places, they have hollowed out immense cavities. The 
fluviatile deposit which rests on this rock, and in which they flow, is called 
" cascalho ;" it is sometimes covered "with large blocks, which evidently belong 
to the itacolumite. "When the hydroxide of iron occurs in the neighboiu-hood, 
it has cemented the upper beds, and changed them into a conglomerate-^the 
"Canga," which is sometimes so hard that it has to be blasted; in it diamonds 
are sometimes found enclosed, of which there are several specimens in Europe. 
The cascalho contains the products of the decomposition of the itacolumite 
and the metamorphic schist; the minerals which it contains are, therefore, 
those of the Servifo da Serra and Servi^o do Campo ; but they are more rolled 
and roimded, and sometiiiies the one and sometimes the other preponderates, 
consequently the characters of this conglomerate are very varied. In the 
