NON-METALLIC MINERALS 



333 



are known in the neighborhood of the diamonds, except at a single place 

 where a small diabase dike breaks through the diamond-bearing quart- 

 zites without affecting perceptibly the surrounding rocks. In spite of 

 their great economic importance, there has never been any systematic 

 work done on the geology of the diamonds of Brazil, and, as Calogeras 

 well remarks, "presque tons les gisements diamantiferes du Bresil ont 

 ete decouverts par hazard/' ^^ 



From private sources I have lately heard reports of the discovery of 

 diamonds at several places in the State of Minas Geraes in peridotite 

 pipes similar to those in which diamonds occur in South Africa. These 

 reports require confirmation. 



Bovet 



Boutain 



Boue 



Bensaude 



Branner 



Campos 



Castelnau 



Claussen 



Cugnier 



Damour 



Dawson, T. 



Die 



Dennis 2 



Derby (Parana) 



Dieulafait 



Dufresnoy 



Engelhardt 



Galvao 



Gorceix 



Glocker 



Haidinger 



Helmreichen 



Heusser u. Claraz 



Hoclieder 



Heuland 



Hussak 



Jacob and Chartrain 



Jannetaz 



Jardim 



Jeremejew 



Kunz 



Lawrence 



Lindsay 



Limonosoff 



Martins 



Mawe 



Moissan 



Nusser-Asport 



Oliveira, F. de P. 



Oliveira (Salobro) 



Pereira 



Pires (Ant. O) 



Porcberon 



Praguer 



Rezende 



Rivot 



Scbwartz (Babia) 



Silva (Babia) 



Vandelli 



Carbonados, or 'black diamonds. — Carbonados are only found in con- 

 siderable numbers in the State of Bahia, where they are associated with 

 ordinary diamonds. ^^ Like diamonds, they are found in stream beds and 

 in old streana deposits, but they have been derived directly from quart- 

 zites. The rocks of the surrounding region from which the carbonados 

 have come are all gently folded, false-bedded, pinkish quartzites, and 

 wherever these quartzites have softened by weathering, the miners have 

 broken them up and washed them for the carbonados thus set free. 

 These carbonado-bearing rocks are possibly of Carboniferous age, but no 

 fossils have yet been found in them and their age is therefore in doubt. 

 The region of the black diamond is hilly and for the most part forest- 

 covered. It is supposed that the carbonados have originated in the same 



'* Rerista Industrial de Minas Geraes II, 5, 15 de .Junho de 1895. 



" Dr. Antonio Olyntho reports carbonados from Rio Abaet€ in the State of Minas 

 Geraes, Annaes da Escola de Minas, number 4, page 115. Rio de Janeiro, 1885. 



XXIII— Bull. Geol. Soc. Am., Vol. 30, 1918 



