M. Pissis on the Andes. 181 



that, ff in a geological point of view, this mountain, ordinarily- 

 spoken of as the volcano of Aconcagua, is in reality not volcanic. 

 It is composed," according to M. Pissis, " from its base to its 

 summit of stratified rocks, the lowest of which is composed 

 of those same porphyries met with at every step on the Andes ; 

 while those on the summit, as judged of from some detached 

 blocks, appear to belong to the cretacean system. It occupies 

 the middle of a great circle situated a little to the east of the 

 line of the Andes, from which it is separated by the valley in 

 which the Rio de Mendoza has its birth. Some syenitic rocks 

 show themselves in the lower part of this circle, which, at the 

 time of my visit, was almost entirely filled with snow, which 

 prevented my satisfying myself whether it contained eruptive 

 rocks of more recent origin." 



The commission remark that, ' ' in spite of the just reserve 

 of M. Pissis, it is difficult to avoid the conclusion that the peak 

 of Aconcagua occupies the bottom of a vast crater of elevation," 

 a conclusion with which few English geologists would concur. 

 Aconcagua is far from being isolated, as M. Pissis mentions 

 three other peaks in its neighbourhood, reaching elevations of 

 6799, 6527, and 6347 meters. "Everything indicates that on 

 that spot the most elevated mountam masses of the American 

 Continent are found." 



A study of the movements by which its present relief was 

 imparted to the South American Continent has led M. Pissis 

 to assert that its stratifications present nine general divi- 

 sions : — 



" 1. The Chilian System, i.e., the most modern of all, and 

 posterior to the marine sands Atacama (remarkable for their 

 deposits of nitrates) and to the formations of transport (terrains 

 de transport) of la Paz. 



" 2. The System of the Principal Chain oe the Andes oe 

 Chili, posterior to the lacustrine and marine deposits of Bolivia, 

 of Chili, and of Patagonia, having a direction exactly N. and 

 S., with appearance of trachytes and argentiferous seams. 



" 3. The System of the Transverse Chains of Chili, pos- 

 terior to the calcareous and saline marls, having a direction 

 approximately E. and W. : Labrador rocks and cupriferous 

 beds. 



" 4. The Western Chain of Chili System, anterior to the 

 saliferous marls, posterior to the ' gres rouges :' direction 

 sensibly the same as in the first system : syenitic rocks, auri- 

 ferous pyrites. 



" 5. The Eastern Chain of Chili System, the elevation of 

 which, contemporaneous with the eruption of quartziferous 

 porphyries, occurred during the Jurassic period. 



" 6. The System of Itacolumi, the appearance of which 



VOL. IV. — NO. III. 



