210 J. C. BRAXXEE OVTLIXES OF THE GEOLOGY OF BKAZIL 



It lias been establislied beyond question that the diamonds and car- 

 bonados foTind in the Bahia region come directly from the false-bedded 

 pink qnartzites.^^ That diamonds are found in the qnartzites at Grao 

 Mogol is equally well established.^^ That the qnartzites of Bahia are the 

 same as those at Grao Mogol is far from being a new theory. It was 

 probably first brought forward by Helmreichen, whose paper was written 

 in 1843 and published in 1846. Helmreichen's theory was based on what 

 he saw at Grao Mogol and on what he heard about the geologic conditions 

 in Bahia.^* But, like many others, he supposed the quartzites of Grao 

 Mogol were the old Paleozoic itacolumites of the Ouro Preto region. He 

 adds that the following places are well known for the occurrence of 

 diamonds : 



1. Burity Quebrada, on the eastern spur of the Serra do Grao Mogol. 



2. Cabeceiras do Corrego da Onca, on the western spur. 



3. Corral de Pedra. on the eastern spur of the Serra do Peixe Bravo. 



4. Serrinha Xova, between Rio Yerde and Eio Par do. 



5. Boqueirao das Barreiras. western spur of Serra do Salto. 



The places mentioned are all on or near the watershed that runs almost 

 due north from Grao Mogol toward the city of Caitete, in the State of 

 , Bahia. and seem to tie up the diamond-bearing quartzites of Minas with 

 the diamond-bearing quartzites of the Chapada diamaniina west of Para- 

 guassii, Bahia. 



It should be kept in mind, in dealing with the geology of this area, 

 that there are several distinct series of quartzites thereabout that may 

 readily be mistaken one for the other, both on account of their general 

 resemblance and on account of their topographic prominence. 



Economic geology of ilie Carhoniferous. — The economic products of 

 the Carboniferous of Brazil are limited to the diamonds and carbonados 

 of Bahia and to the diamonds of that part of northern Minas Geraes 

 which is supposed to be correlated with the diamond-bearing quartzites 

 of Bahia. The evidences of the origin of the diamonds and carbonados 

 are given briefly under the head of "Carboniferous'' and under the State 

 of Bahia. The diamond-bearing beds are not all equally rich. 



^ O. A. Derby : The geology of the diamond and carbonado washings of Bahia. Eco- 

 nomic Geology, vol. i. November-December. 1905. pp. 134-142. 



J. C. Branner : The economic geology of the diamond-bearing highlands of Bahia. 

 Engineering and Mining Journal. May. 1909. pp. 87, 981. 1031. 



Roderic Crandall : Notes on the geology of the diamond region of Bahia. Brazil. 

 Economic Geology. May. 1919, vol. xiv. pp. 220-244. 



1^ Virgil V. Helmreichen : Geognostische Verkommen der Diamanten . . . auf der 

 Serra do Grao Mogol. Wien. 1846. 



H. Gorceix : Gisement de diamants de Grao Mogol. Bui. Soc. Geol. de France, vol. 

 xii, pp. 538-545. Paris, 1884. 



" T. von Helmroichen : Geognostische Verkommen der Diamanten, etc., pp. 63-65. 

 Wien, 1846. 



