DIAMOxND: OCCURRENCE IN BRAZIL 159 



on the left bank by its tributary the Rio Andrada. Into the Rio de Sao Francisco flow 

 also the Rio Indaia, the Bambuy, the Barraehudo, as well as the Paricatii, with its tributaries 

 Santo Antonio, d' Almas, de Somno, de Catinga, de Prata, and others. The diamonds of 

 this region were discovered by unlicensed searchers (garimpeiros) in 1785, who worked at 

 first without a concession ; in the Rio Abaete they found one of the lai'gest of Brazilian 

 diamonds, which weighed 138^ carats. Although in 1791 there were as many as 1200 

 licensed workers at the place, the deposits seem to have been very quickly worked out 

 subsequent to the year 1795, and in 1807 work here practically ceased. 



This district embraces a stretch of country on the eastern slope of the Serra da Mata 

 da Corda, about 300 miles long, and it is here that the rivers mentioned above have their 

 sources. On the western side of the same range, still in Minas Geraes, but near the border 

 of the State of Goyaz, is the district of Bagagem, having about the same length as the 

 district of the Rio Abaete, the two districts having together a width of about 250 miles. 

 The whole area embraced by these districts, though it has been only partially explored, has 

 yielded a large number of diamonds, many of which are of considerable size. These include 

 a stone of 120f carats, and also the famous " Star of the South," the largest of Brazilian 

 diamonds, which was found in 1853, and in its rough condition weighed 254J carats. 



A new diamantiferous deposit, which, however, does not appear to be very rich, has 

 recently been discovered and worked in the district at Agua Suja, about twelve miles south 

 of Bagagem. The diamonds are here associated with blocks of rock, identical with that 

 which occurs in situ not far away, together with much magnetite and also ilmenite, decom- 

 posed perofskite, pyrope, and rutile. Some of these minerals, more especially the perofskite 

 and pyrope, have not hitherto been found associated • with diamond at any other Brazilian 

 locality. This association of minerals recalls the mineral constituents of the " blue ground " 

 of Kimberley in South Africa, which will be described later, as will also the various minerals 

 hitherto found in Brazil associated with diamond. 



One other diamantiferous district in the State of Minas Geraes remains to be mentioned, 

 namely, that of Grao Mogol (Grao Mogor), which is situated about 180 miles north of 

 Diamantina, in a mountain range to the north-west of, and on the left side of, the Rio 

 Jequetinhonha. Although this district was first searched in 1813 diamonds were not found 

 here until 1827 ; it is remarkable as being the only locality at which diamonds occur in the 

 solid sandstone, which, at one time, was thought to be their original mother-rock. Though 

 the yield from this district is now small, it was formerly rather considerable, 2000 people 

 being employed in the industry in 1839. 



The geological relations of the diamantiferous districts of the State of Minas Geraes, 

 especially that of Diamantina, have been frequently investigated, and, at least in the case of 

 the latter, are fairly well understood, though many doubtful points still await elucidation. 

 The investigations which have been made are due, at the beginning of the nineteenth century, 

 to L. von Eschwege ; a little later to Spix and Martius ; in the fifties, first to Heusser and 

 Claraz and then to Claussen and Helmreichen ; and in recent times to various geologists 

 resident in Brazil, namely, Gorceix, De Bovet, Orville A. Derby, and others. 



We learn from their observations that the principal rock in the Serra do Espinha^'o is 

 usually a thinly laminated sandstone or quartzite, the laminae bearing numerous scales of pale 

 green mica on their surface. Some of the thin laminae or slabs are so peculiarly constituted 

 that they can be bent without being broken, such specimens being hence described as flexible 

 sandstone. TTie increased size of the quartz grains and pebbles renders the rocks in places 

 more coarse-grained in character, s6 that it resembles a conglomerate rather than a sandstone. 

 This laminated sandstone, which is of great geological antiquity, is usually regarded as a 



