STRATIGRAPHIC GEOLOGY 209 



lack confirmation. Dr. Lisboa^^ credits Gonzaga de Campos with the 

 report of Carboniferous extending south and west from the Tapajos area 

 to Eio Theodoro just north of south latitude eight degrees, as indicated 

 by dotted lines and the question-mark. Eocks in Sao Paulo and Parana 

 formerly called Carboniferous by Derby are now known to be of Permian 

 age, while the diamond-bearing beds of Bahia referred provisionally to 

 the Carboniferous by Branner have not yet yielded any fossils, and the 

 age of those particular beds must still, therefore, be considered as 

 doubtful. 



In the Amazon region the Carboniferous rocks are shales, sandstones, 

 and limestones ; the fossils are found in the limestones and are all marine 

 forms. At Itaituba the limestone is eight meters in thickness. The total 

 thickness of these Carboniferous rocks in the Amazon basin is about 600 

 meters. No coal-bearing beds have been found in them. 



The Bahia beds referred with doubt to the Carboniferous are the pink- 

 ish quartzites, sandstones, and conglomerates from which diamonds and 

 carbonados are obtained. The rocks are gently folded over much of the 

 diamond district and in some places they are closely folded and faulted. 

 On account of their resistance to weathering they have a marked effect 

 on the typography of the region in which they occur. 



These quartzites, which are here tentatively referred to the Carbonif- 

 erous, are of much geologic importance and interest aside from the fact 

 that they are the rocks from which the diamonds and carbonados of 

 Brazil are derived. 



Bearing in mind that the Carboniferous age of the group of rocks here 

 discussed has not been definitely settled, and that we have no paleonto- 

 logic evidence of their age, it is nevertheless important to bring together 

 such evidence as we have of the age, character, and distribution of this 

 series. 



In the State of Bahia the structural features of these beds, their rela- 

 tion to those above and below them, and their areal distribution are fairly 

 well outlined in the papers of Branner, Crandall, and Williams. But 

 between the Chapada diamantina of Bahia and the diamond fields of 

 Minas Geraes is an area about which we have very little geologic infor- 

 mation, and practically none that would enable us confidently to tie to- 

 gether with the necessary structural details the two regions. Certain 

 facts, however, lend strong support to the theory that the diamond-bear- 

 ing quartzites of the Bahia region are simply the northward extension of 

 the diamond-bearing quartzites of Minas that are exposed and known to 

 contain diamonds at Grao Mogol. These facts are here brought together. 



O problema do combustivel nacional. Rio, 1916, fig. xiv. 



