ranges. These ranges are widely separated and enclose a broad, greatly elevated plateau, 125 miles in breadth in the northern part, and nearly 300 miles in the south, with an altitude of almost 13,000 feet. The plateau of the Andes has here the greatest lateral extent and altitude in the entire system. The western range has an average altitude of 15,000 feet, while the Eastern, or Cordillera Real, is still higher, having peaks exceeding 20,000 feet; among them are Illampu, 21,490 feet; Illimani. 21,030 feet; Ancohuma, 21,490 feet; Haina, 20,171 feet; Paniri, 20,735 feet: Licancaur, 19,521 feet; Sajama, 21,047 feet; Isluga, 17,000 feet: and Cacaca, 20,250 feet, all of them near Lake Titicaca. East of this range are several lower subsidiary ranges, which form a complicated system. Lake Titicaca drains southeastward into Lake Poopo, a sink which collects the waters from a large area of the plateau. In the Cordillera Real and the lesser ranges to the east, rise tributaries of the Madeira, one of the main branches of the Amazon, and of the Pilcomayo, tributary to the Plata.
Chile and Argentina. The broad, high plateau, with its bordering ranges and subsidiary eastern ranges of Bolivia, extends southward into these countries, gradually narrowing and decreasing in altitude, until in latitude 32° the Andes become reduced to a single range, except for spurs and outliers, most of which are of comparatively little importance. In the northern part the altitude of the ranges decreases greatly, Juncal, in latitude 26°, having a height of 17,530 feet, and Copaipó volcano, 19,700 feet. Farther south, in the neighborhood of Santiago. the mountains again become loftier. Here are Mercedario, 22,315 feet; Tupungato, 20,286 feet; San Jose, 20,020 feet; and Aconcagua, 22,860 feet; this latter peak is the highest summit of the entire system, and of the whole continent, so far as known. Still further south, the range again diminishes in height. In latitude 34° is Maipo volcano, 17,670 feet: in latitude 36° is Descabezado, 12,760 feet; in latitude 42° is Tronador volcano, 9790 feet. Here begins the remarkable fiord coast, which extends south to Cape Horn. The heavy precipitation on the west side of the range here produced in past times extensive glaciers, which chiseled the mountains far down below sea level, producing many islands, and an intricate system of mountain-walled channels. These glaciers have been able, by reason of their rapid descent, to cut back their heads across the range in many places, so that now, after their recession, many of the streams which have succeeded them rise far to the east of the Andes, upon the plains of Argentina, and flow through the range to the Pacific. In this region the mountains become still lower, their height ranging from 4000 to 8000 feet, until they finally disappear at Cape Horn.
The lower limit of perpetual snow, although an extremely indefinite line, varying from year to year with exposure and precipitation, has in general, in equatorial regions, an altitude of about 15,500 feet, but ranges a thousand feet on each side of this figure, being higher on the east and lower on the west side of the range. In other words, it is higher where the precipitation is abundant, and lower where it is scanty. It diminishes as the latitude increases, being about 13,000 feet in the latitude of Santiago, and falling to 3000 feet near the southern point of the continent. Glaciers are found on all the high peaks, even those in equatorial regions, which exceed 13,000 feet in height. Here, however, they are small, descending the mountain slope only a few thousand feet. In southern Chile, on the west side of the range, are many of considerable size, originating upon mountains of inferior height, and descending to sea level, even entering the sea, at the heads of fiords.
Volcanoes. One of the striking features of the Andes is its great number of active and extinct volcanoes. Probably not over sixty are now known to be active, but the extinct ones are numbered by hundreds, and have played a very important part, though a secondary one, in creating the present conformation of the mountain system. Three principal centres of volcanic activity are recognized: one in the Andes of the north, in Colombia and Ecuador, extending in latitude from 5° N. to 3° S.; a second in Peru, Bolivia, and northern Chile, extending in latitude from 15° to 28° S.; and a third in central Chile, extending from 32° to 40° S. The highest peaks of the Andes are of volcanic formation, and their peculiar conical forms are distinctive features of the Andean landscape. Many of the most prominent and highest ones have been mentioned; it remains to speak of those which are now active, or which have been active within historic times, and briefly describe their eruptions.
The northern group, mainly comprised in Ecuador, is the most imposing collection of active and extinct volcanoes on earth. Of these, Cotopaxi, Tunguragua, Sangai, and Pichincha have repeatedly been in eruption in historic times, but most, if not all, of the others have for a long time been quiescent. The Altar, a truncated mountain, 17,736 feet in height, is said to have once been the highest in the region, but after a long period of eruption it collapsed within itself. Ruiz, in Colombia, is still smoking, and Tolima is not quite extinct, but as late as 1829 was in eruption. In 1849 Purace, in southern Colombia, suddenly exploded, flooding the neighboring country, and covering it with ashes. A similar eruption took place in 1869. Imbabura, in Ecuador, is said to have discharged a deluge of mud and water at the time of the great earthquake in 1868. Antisana is reported as having been in eruption in 1590, and even now sulphurous fumes arise from it. Cotopaxi, always smoking, has been repeatedly in eruption, although its great eruptions have occurred at intervals of centuries. The last one was in 1877. Tunguragua also is active at irregular intervals, the latest eruption being in 1886. Sangai sends off steam constantly with tremendous force and noise. Pichincha has, since its eruption in 1660, given off nothing but steam and a little ashes.
The middle volcanic group is found in both the eastern and western Cordilleras; in Peru it includes Sarasara, Atchatayhua, Corupuna, Ampato, Chachani, and Misti, all now quiescent. Omate and Tutupaca have been in eruption in historic times; indeed, the former was one of the most active in Peru. In Bolivia are Mount Sorata, or Illampu, Sajama, Aucaquilcha, Chachaconiani, Huiana, Cacaca, Mesada, and Illimani, while in northern Chile are many volcanic cones, some of great height; among them are Tacora, 19,750 feet, Chipicani, Pomerape, Pariuacota, Iquima, 20,275 feet, and Toroni, 21,340 feet, all in the western range. In the eastern
