Chiquitian^ Bolivian^ Columbian, and Fuegian Systems, 121 



culminating points of an axis of granatoidal rocks, running 

 from SE. to NW., and which having doubtless been elevated 

 through a great crevasse, has been the cause of the elevation 

 of the whole Bolivian system. 



This elevation took place after the deposition of the trias, as 

 is shewn by the triassic beds which M. D'Orbigny has seen 

 in an inclined position, and at a height of more than 4000 

 yards above the sea. The triassic formations form the last 

 upraised beds in the different localities where they have been 

 observed in Bolivia. At all the parts of the Bolivian system 

 where M. D'Orbigny has seen them, when they are covered, 

 they are so only by horizontal beds of the Pampean formations, 

 or by modern alluvia, products which are entirely terrestrial, 

 and not marine. It thus appears certain that the Bolivian 

 system has assumed the characteristic features of its outline, 

 subsequently to the period of the triassic formations. We 

 may also conjecture that this phenomenon took place before 

 the deposition of the Jurassic and cretaceous formations, for 

 otherwise these formations would have been deposited on the 

 trias of Bolivia, and would have been upraised along with it. 



Probably, therefore, it was between the triassic and the 

 Jurassic periods, or nearly at that epoch of our European 

 chronology, that the whole mass comprised between the west- 

 ern plateau of Bolivia and the plains of Santa-Cruz and Moxos 

 was elevated above the ocean. 



Endeavouring to complete, at least in a conjectural manner, 

 the tableau of the great geological phenomena of which South 

 America has been the theatre and the product, M. D'Orbigny 

 is led to suppose, from the observations of the latest travellers, 

 that two great dislocations took place during the great creta- 

 ceous period : the one, represented by the Columbian system, 

 running from N. 33° E. to S. 33° W., formed the mountains of 

 Suma-paz and of Quindiu, elevating the cretaceous formations 

 of the plateau of Bagota ; the other produced the Fuegian 

 system, which occupies the western portion of Terra del 

 Fuego, and runs from N. 30° W. to S. 30° £. 



The effect of these different and successive phenomena 

 must have been to elevate above the ocean the principal 

 mountainous centres of South America ; but these different 



