254 J. C. BRAXXER OUTLIXES OF THE GEOLOGY OF BRAZLL 



MARAyniO 



Previous investigations. — In the preparation of the geographic base 

 for the State of Maranhao I have had the benefit of the coordinates de- 

 termined by Dr. Arnaldo Pinienta da Cunha and pnbhshed in the Boletim 

 Official do IMinisterio da Industria. Yiacao e Obras Publicas. 1"^ anno, 

 tomo II, page 158, Eio de Janeiro, 1909. 



The most valuable papers on the geology of Maranhao are those of Dr. 

 M. Arrojado E. Lisboa, the notes of Spix and Martins, and those of 

 James W. TTells. The interior of the state is bnt little explored. On the 

 lower Tocantins I hare followed Castelnan by referring his sandstones 

 and shales to the Permian of Lisboa. 



General geoJogy. — Archean rocks are known in Maranhao along Eio 

 Gnrupy, on the lower portion of the Tnry-assu, and along a short piece 

 of Eio Itapicnrn between Codo and Coroata. It is possible that there is 

 also a belt of Archean exposed along Eio Grajahii near four degrees south 

 latitude, where Wells reports a hard dark "greenstone" very similar to 

 that at Chapada.^- 



The oldest known rocks in Maranhao after the Archean are supposed 

 to be the Permian sediments, which cover nearly half of the state. These 

 Permian beds, as described by Dr. Lisboa. are here mentioned in their 

 natural order: 



Unconforrnit}/ at the Top of the Per mi an 



Thickness in 

 meters 

 7. Green and chocolate-colored shales, limestones, and white sandstones. 3 



6. Sao Bartholomeu sandstone, ashen gray, false-bedded 50 



5. Pisolitic rock, mostly white sandstone ? 



4. .Jaboti red sandstone, with pui-ple spots =150 



3. Mendes sandstone, ashen gi'ay to white ? 



2. Ashen gray marly shales and calcareous beds '. ? 



(Interval not seen.) 

 1. Bituminous shales. 



These sedimentary beds are nearly horizontal, and are cut here and 

 there by dikes and interstratified with sheets of diabase. 



Xext above the Permian beds is the Mearim series of Lisboa, and pro- 

 visionally referred by him to the Triassic. These beds are principally 

 red sandstones having a thickness of 100 meters. In places they contain 

 flows of amygdaloidal trap. 



In the Serra Vermelha above the city of Grajahii these beds dij) locally 

 west-northwest, and the red sandstone, with the included trap, has a 

 thickness of 235 meters. 



^- J. W. Well? : Three thousand miles through Brazil, vol. ii. p. 291. London. 18S6. 



