Brazilian, Pampean, and Itacolumian Systems. 119 



of the transition series, " whose deposition/* he says, " was 

 interrupted by commotions which elevated it at some parts to 

 a height of a thousand or eleven hundred yards above the level 

 of the sea, and produced at other points large fissures running 

 east and west, through which escaped diorites, that spread 

 themselves like lavas, and modified the rocks they met with. 

 The most elevated mountains of Brazil, those of the province 

 of Minas Geraes, viz. Itacolumi, Caraca, Morro Itampe, and 

 the plateaus to the south of San-Paolo, belong to this 

 aoulevement, which gave the beds an EW. direction, and 

 communicated to the surface its present form."* 



M. D'Orbigny terms the whole of the ridges formed by this 

 dislocation Itacolumian system. He would be induced to con- 

 nect with it the mountains of the Malouine Islands, which 

 he designates by the name of the Malouinian system, if it 

 should be ascertained that these mountains are formed of 

 Silurian beds having an EW. direction. 



Thus, according to him, the gneiss islands, which form the 

 most ancient portion of the American surface, were extended 

 towards the west by dislocations, which took place after the 

 deposition of the transition formations, while, perhaps, new 

 points were elevated from the bosom of the waters in the 

 Malouine Islands, and near Cochabamba, in Bolivia. This 

 phenomenon appears to have been anterior to the deposition 

 of the carboniferous system, subsequently to which new dis- 

 locations occurred, whose most marked traces were observed 

 by M. D'Orbigny in the province of Chiquitos. 



The hills of this province have gneiss for a fundamental 

 rock, on which repose silurian and devonian beds ; and these 

 are covered by sandstones referred by M. D'Orbigny to the 

 upper layers of the carboniferous system, and flanked by triassic 

 beds, and by tertiary deposits. These hills present a general 

 parallelism which renders them a well characterised system, 

 having a direction from ESE. to WNW., and to which be- 

 long the chains of Parecys, of Diamantino, and of Cuyoba, in 

 the western portion of Brazil. M. D'Orbigny terms the whole 



* Pissis, Comptes rendus des Seances de rAcademie des Sciences, 

 t. xiv. p. 1044. 



