THE GEOLOGY OF THE DIAMOND AND CARBONADO 

 WASHINGS OF BAHIA, BRAZIL." 



By Orville A. Derby.* 

 [Translated by J. ('. P.ranner. ] 



A trip to the diamond washings of Brazil recently made by the 

 writer afforded an opportunity for obtaining a general idea of the 

 geologic structure of the basin of Rio Paraguassu, which in its upper 

 part includes the principal diamond region of the State of Bahia — the 

 so-called " Chapada Diamantina," or diamond plateau. 



The Paraguassu River crosses four regions different from one 

 another in their geologic make-up and in their topographic and eco- 

 nomic features. The first of these regions includes the entire district 

 about the headwaters of the river and its principal tributary, the 

 Santo Antonio, and extends as far as the falls of Passagem de 

 Andarahy ; the second extends from this point to the village of Bebe- 

 douro, about 70 kilometers by the wagon road below Passagem and 

 20 kilometers above the terminal station on the railway at Bandeira 

 de Mello; the third extends from Bebedouro to the city of Marago- 

 gipe, with a width of about 300 kilometers; and the fourth from the 



o Reprinted, by permission, from Economic Geology, Vol. I, No. 2, November- 

 December, 1905. Economic Geology Publishing t'ompany, Lancaster, Pa. 



& Prof. O. A. Derby, for many years State geologist of Sao Paulo, Brazil, was 

 lately employed by the State of Babia to report upon the geology of the part of 

 tbe State from which the carbonados are derived. The present paper is trans- 

 lated from the report made to the governor and published in the Portuguese 

 language in the Diario da Bahia of June 1 and June 3, 1905. It is the most 

 important paper thus far published upon the geology of the carbonados. It does 

 not deal with the origin of the diamonds and carbonados, for the deposits men- 

 tioned are clearly secondary, but the geologic structure of the region is of the 

 greatest economic importance in connection with prospective mining. Other 

 papers by Mr. Derby upon diamonds are as follows : 



1. " Geology of the diamond," Am. Jour. Sci.. XXIII, 97-99, 1882. 



2. " Modes of occurrence of the diamond in Brazil," Am. Jour. Sci., XXIV, 

 34-^2, 1882. 



3. " The genesis of the diamond," Science, IX, 57-58, 1887. 



4. " Brazilian evidence on the genesis of the diamond," Jour. Geol., VI, 121- 

 146. Chicago, 1898. 



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