166 



THE GEOLOGIST. 



various approximations to an earthy mass, which also contains diamonds, and 

 which is designated " terra." The "barro'^and "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 following 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 the barro and the gurgulho do 

 campo is exactly the same. We have, besides, examined the stony fragments 

 which 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 full of water ; it hardens how- 

 ever on exposure. The diamonds it contains do not detach themselves at first, 

 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 1855 has yielded richer and more regular products, and while we 

 were there preparations were being made to open another. Near Quinda there 

 are many workings of the gurgulho 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 

 mel hods, 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 tins 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 

 jo i he itacolumite. \\ hen the hydroxide of iron occurs in the neighbourhood, 

 it has cemented the upper b^fls, and changed them into a conglomerate — the 

 " ( langa," w Inch is sometimes so hard that it has to be blasted ; kit 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 Servico da Serra and Servico do Campo; but they are more rolled 

 and rounded, and sometimes the one and sometimes the other preponderates, 

 consequently the characters of this conglomerate are very varied. In the 



