PHYSICAL FEATURES OF CHILI. 



411 



Cordillera of the Andes consists chiefly of metaraorphic porphyries dating from the 

 secondary period, and elsewhere represented by limestones, marls and sand- 

 stones. Volcanic rocks, such as trachytes and modern lavas, have also cropped 

 out in many parts of the primitive formations. 



The longitudinal valley comprised between the two mountain ranges is covered 

 with lacustrine strata deposited in tertiary times, and in their composition resem- 

 bling the formations of the Atacama desert and those traversed by the Desagua- 

 dero of Lake Titicaca. They consist of sandstones and clays, covered with a 

 layer of rocks and gravels rolled down from the Andes by the torrents and ava- 

 lanches. Here fossils are rare, although some traces of vegetation are met, while 

 the remains of the Andean mastodon occur in the alluvia filling the cavities of the 

 surface gravels. 



The central knot, where converge the Atacama, Bolivian and Argentine 

 branches, is dominated by the so-called " volcano " of Copiapo, 19,700 feet high. 



Fig. 154. — Paeallel Cobdilleear of the Chilian Ani>es. 

 Scale 1 : 16,500.000. 



Concepcion 



>.# 1 i' U'j 



;o,ooi) 



16,500 

 13,000 

 9,850 

 -j 6,550 



3,300 



310 Miles. 



The name is so far justified that vast deposits of sulphur are found in the vicinity 

 of the mountain. South of Copiapo the Argento-Chilian cordillera expands to 

 a broad plateau, where the range presents but a slight relative altitude, and is 

 crossed by low passes ; which, however, are difiicult to surmount owing to the long 

 spaces swept by biting winds and fierce storms. One of the mosc frequented of 

 these passes, connecting the Argentine mining regions of Famatina with those of 

 Copiapo in Chili, is the Portezuelo de Come Caballos, " Horse-Eater's Pass," 14,530 

 feet hiffh Other tracks cross the Andes farther south at the Pulido and Pircas 



o • 



Negras passes. 



In these regions the mass of the cordillera consists of yellowish earthy heights 

 rolling away without apparent order, and marked with a few patches of snow. 

 The bleak " pampas of the cordillera " are very dangerous to cross in the winter 

 months from May to November, and especially at the turn of the seasons, owing 



