120 Geology of South America. 



the Chiquitian system, and considers it as posterior to the last 

 carboniferous layers, and as anterior to the trias, seeing that 

 the last beds which are seen to be deranged belong, accord- 

 ing to him, to the carboniferous system. 



The production of a great system of dislocations in South 

 America at this epoch, is confirmed, according to M. D'Or- 

 bigny, by the immediate contact of the variegated clays of 

 the region situated to the east of Cochabamba, with the de- 

 vonian formations. This contact seems to announce a denu- 

 dation of the carboniferous formations anterior to the deposi- 

 tion of the triassic series. 



The hills of the Chiquitian system nearly join the moun- 

 tains of Brazil at the base of the Andes. We have thus a 

 new appendage added to that already formed by the Itacolu- 

 mian system. When we cast our eyes over the geological 

 map of Bolivia prepared by M. D'Orbigny, it may appear at 

 the first glance that there are numerous features of resem- 

 blance in the arrangement of the formations of the hills of 

 Chiquitos, and of the eastern chain of the Andes. However, 

 the direction which predominates in the mountains of Chi- 

 quitos is not exactly the same as that of the ridges occurring 

 on the flanks of the Cordillera, to the south-east of the 

 plains of Moxos and of Santa-Cruz-de-la-Sierra, and the 

 height of the two masses of mountains is too different to make 

 it natural to suppose that they should be referred to one and 

 the same epoch of soulevement. 



The colossal mountains which rise above the north-east of 

 the lake of Titicaca, and with which is connected the whole 

 eastern region of the Cordilleras, from the fifth to the twen- 

 tieth degree of south latitude, or, to speak more correctly, the 

 Andes properly so called, the Antis of the ancient Incas, form 

 a distinct system, to which M. D'Orbigny has given the name 

 of Bolivian system. The mean direction of this system, very 

 different from the directions which prevail in the rest of the 

 Cordilleras, is from SE. to NW. The ridges composing it 

 consist of elevated beds of the silurian, devonian, carbonife- 

 rous, and triassic formations. This celebrated Nevados of 

 Illimani and of Sorata, ascertained by Mr Pentland to be 

 the most elevated summits of the New World, are the two 



