300 J. C. BEAXXER OUTLINES OF THE GEOLOGY OF BRAZIL 



and end with the remark that the rocks are granites and gneisses. The 

 most comprehensive papers are those of Pissis. EschTvege, Caldclengh, 

 Derby on the ernptives in Eio de Janeiro, and of Alberto Paes Leme on 

 '^08 gneiss do Eio de Janeiro.'' Others are mostly field-notes; such are 

 those of Bnrmeister. Hartt, Burton, Collie, Eschwege, and D'Orbigny. 



The island of Trindade, in south latitude 20^ 30', west longitude 29° 

 25', belongs to the Federal Union and, together with the Federal District, 

 is here included with the State of Eio de Janeiro. The island is shown 

 as an inset on the map of Brazil. 



General geology. — ^Archean rocks cover all of the state except a narrow 

 belt of Tertiary and Quaternary sediments on the coast and some isolated 

 patches of Tertiary lake deposits in the valley of the Parahyba. 



Of the geologic structure of the State of Eio de Janeiro but little is 

 known, for the character of the rocks, the depth of decomposition, and 

 the presence of dense forests render field-work difficult and unsatisfac- 

 tory. The only attempt to work out the strucuire of any considerable 

 part of the geology about the city of Eio de Janeiro is reported in the 

 paper of Alberto Paes Leme, entitled •"Estudo geologico de uma parte do 

 districto federal,'" cited in the bibliography that follows. It seems evi- 

 dent at a glance that the granites, gneisses, schists, and eruptives of the 

 region have been much faulted, profoundly decomposed, and extensively 

 denuded. The Tertiary lake beds referred to have been reported only 

 from two places in the State of Eio de Janeiro, namely, Barra Mansa and 

 Eezende. They are evidently the eastward prolongations of the Tertiary 

 beds found at Taubate. but separated by denudation from the larger 

 original areas. 



At many places near the coast lakes have been shut in by Quaternary 

 and late sediments that have been thrown into the embayments by the 

 ocean. The geography of the coastal region is especially interesting, and 

 a careful study of it would throw much light on the geological history of 

 the region and of the country. But little attention has been given to this 

 subject, however. It is spoken of briefly in Branner^s "Stone reefs of 

 Brazil,'' at pages 12L 128, and 132. 



The uninhabited island of Trindade is entirely of eruptive rocks — 

 phonolites. 



Economic geology. — The economic geologic products of the State of 

 Eio de Janeiro, including the Federal District, are limited chiefly to 

 building stones, marbles, and ceramic clays. 



The quarrying industries of the state, and especially those in and near 

 the city of Eio de Janeiro, are of great importance and have had a strik- 

 ins: influence on the character. disniitA-. and stabilitv of the architecture 



