GENERAL AND ECONOMIC GEOLOGY 2(31 



Economic geology. — That the mineral resources of Matto Grosso are 

 but little known is probably due, to some extent at least, to its difficult 

 geographic position and to the fact that the geology of large areas in the 

 state has never been studied. Hitherto it has produced gold and dia- 

 monds, and it is probable that gold can be dredged along some of the 

 streams. Iron and manganese are said to exist in large quantities at 

 Urucum (Evans), where they are near river transportation. A descrip- 

 tion of the geology of the iron and manganese ores shows a remarkable 

 resemblance to that of Minas Geraes. The order of the rocks is as follows, 

 from below upward : gneiss, mica schist, itacolumite, manganese and iron, 

 mica schists, limestone. The beds are mostly horizontal. The hematite 

 iron is said to be from 10 to 15 meters thick and the manganese is from 

 1 meter to 2.4.'^^ 



From an unpublished private report on the Frucuni mines by Dr. 

 Lisboa, and dated March, 1918, I am permitted to quote his description 

 of the geology : 



"In general the tJrucum Mountains consist of a series of sedimentary rock 

 to wMcti I gave tlie name of Jacadigo series in 1907, and wliich consists of 

 two characteristic formations. The lower one is of rough arkose becoming 

 finer toward the top ; the upper one, which is clearly separated from the lower 

 one, consists of ferriferous sandstones. The iron and manganese occur in par- 

 allel beds in this upper division." 



The Jacadigo series, regarded by Dr. Lisboa as pre-Devonian, is said to 

 have a total thickness of from 250 to 500 meters; the rocks beneath them 

 are granites and mica schists. 



The manganese beds he reports as varying in thickness from less than 

 one meter to five meters. His analyses show the manganese ores to run 

 as high as 58.4 per cent of metallic manganese, or 60.8 per cent of man- 

 ganese and iron together. 



Geologic Maps of Matto Grosso 



Evans, 1894. — Dr. J. W. Evans' paper on the geology of Matto Grosso, 

 published in the Quarterly Journal of the Geological Society of London, 

 volume L, pages 85-104, contains a small map showing the general geol- 

 ogy of a large area along the Eio Paraguay between Coimbra and Dia- 

 mantino. The map is on a scale of 1 to 2,500,000 (it is erroneously given 

 on the map itself) and nine divisions of the geology are shown. 



Lisboa, 1909. — Dr. Miguel A. Lisboa's report on the geology along 

 the railway route between Sao Paulo and Matto Grosso, published at Eio 



" Publio Ribeiro fe H. Kilburn Scott: O manganez no Brazil, p. 18. Rio de Janeiro. 

 1902. 



