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 average height of 13,000 ft. The connexion of this system with that of the Rocky Mountains, which has been pointed out by many writers, has received much support from the discovery of the extensive eruptions of granite during Tertiary times, extending from the southern extremity of South America to Alaska. The Andean range is composed of two great principal chains with a deep intermediate depression, in which, and at the sides of the great chains, arise other chains of minor importance, the chief of which is that called the Cordillera de la Costa of Chile. This starts from the southern extremity of the continent, and runs in a northerly direction, parallel with the coast, being broken up at its beginning into a number of islands, and afterwards forming the western boundary of the great central valley of Chile. To the north this coastal chain continues in small ridges or isolated hills along the Pacific as far as Colombia, always leaving the same valley more or less visible to the west of the western great chain.

Of the two principal chains the eastern is generally called Los Andes, and the western La Cordillera, in Colombia, Peru and Bolivia, where the eastern is likewise known as Cordillera Real de los Andes, while to the south of parallel 23° S. lat. in Chile and Argentina, the western is called Cordillera de Los Andes. The eastern disappears in the centre of Argentina, and it is therefore only the Cordillera de los Andes that is prolonged as far as the south-eastern extremity of the continent. The Cordillera de la Costa begins near Cape Horn, which is composed principally of crystalline rocks, and its heights are inconsiderable when compared with those of the true Cordillera of the Andes. The latter, as regards its main chain, is on the northern coast of the Beagle Channel, in Tierra del Fuego, bounded on the north by the deep depression of Lake Fagnano and of Admiralty Sound. Staten Island appears to be the termination to the east. The Cordillera of the Andes in Tierra del Fuego is formed of crystalline schists, and culminates in the snow-capped peaks of Mount Darwin and Mount Sarmiento (7200 ft.), which contains glaciers of greater extent than those of Mont Blanc. The extent of the glaciers is considerable in this region, which, geographically, is more complex than was formerly supposed. Although, in the explored portion of the Fuegian chain, the volcanoes which have been mentioned from time to time have not been met with, there seem to have existed to the south, on the islands, many neo-volcanic rocks, some of which appear to be contemporaneous with the basaltic sheet that covers a part of eastern Patagonia. The insular region between Mount Sarmiento and the Cordillera de los Andes, properly so called, i.e. that which extends from Magellan Strait northwards, is not fully explored, and all that is known of it is that it is principally composed of the same rocks as the Fuegian section, and that the greater part of its upper valleys is occupied by glaciers that reach down to the sea amid dense forest.

As Admiralty Sound and Lake Fagnano bound the Cordillera to the north in Tierra del Fuego, so at the eastern side of the Cordillera in the southernmost part of the continent there is a longitudinal depression which separates the Andes from some independent ridges pertaining to a secondary parallel broken chain called the pre-Cordillera. This depression is occupied in great part by a series of lakes, some of these filling transversal breaches in the range, whilst others are remains of glacial reservoirs, bordered by morainic dams, extending as far as the eastern tableland and corresponding in these cases with transversal depressions which reach the Atlantic Ocean. Between the larger lakes, fed by the Andine glaciers of the eastern slope of the Southern Andes, are Lakes Maravilla, 100 sq. m., and Sarmiento, 26 sq. m., 51° S. lat., which overflow into Last Hope Inlet; Argentino, 570 sq. m., 50° S. lat.; and Viedma, 450 sq. m., 49° 30′ S. lat., which empty into the river Santa Cruz; the fjordian Lake San Martin, 49° S. lat., and Lakes Nansen, 18 sq. m.; Azara, 8 sq. m.; and Belgrano, 18 sq. m., which are dependents of Lake San Martin (380 sq. m.), and Lakes Pueyrredon (98 sq. m.) and Buenos Aires (700 sq. m.), which now overflow into the Pacific, through one of the remarkable inlets that are found throughout the Cordillera, the Calen Inlet, which is the largest western fjord of Patagonia. To the north of Lake Buenos Aires there is Lake Elizalde, which, while situated on the eastern slope, sends its waters to the Pacific Ocean, and Lakes Fontana (30 sq. m.) and La Plata (34 sq. m.), 45° S. lat., which feed the river Senguerr, which flows to the Atlantic. Lake General Paz (66 sq. m.) on the eastern slope of the Andes, at 44° S. lat., is the principal source of the Palena river, which cuts all the Cordillera, while Lakes Fetalauquen (20 sq. m.) Menendez (28 sq. m.), Rivadavia (10 sq. m.), and other smaller lakes, also situated between 43° 30′, and 42° 30′ S. lat. on the eastern slope send their waters to the Pacific by the river Fetaleufu which cuts through the Andes by a narrow gorge. The waters of Lake Puelo (18 sq. m.) likewise flow into the same ocean through the river of that name, which also cuts the Cordillera, and of which the principal affluent likewise drains the waters of a system of small lakes, the largest of which, Lake Mascardi, measures 17 sq. m., which in comparatively recent times formed part of the basin of Lake Nahuel-Huapi (207 sq. m.), 41° S. lat. An extensive area of glacial deposits shows that a sheet of ice formerly covered the whole eastern slope to a great distance from the mountains. To the west another sheet reached at the same time the Pacific Ocean.

From the Strait of Magellan up to 52° S. lat., the western slope of the Cordillera does not, properly speaking, exist. Abrupt walls overlook the Pacific, and great longitudinal and transversal channels and fjords run right through the heart of the range, cutting it generally in a direction more or less oblique to its axis, the result of movements of the earth’s crust.