Encyclopædia Britannica, Ninth Edition/Andes
ANDES. The Andes form a mountain chain second only to the Himalayas in the vastness of its proportions, and possessing many remarkable peculiarities. The origin of the name appears to be unknown, although numerous meanings have been authoritatively assigned to it. It has been variously supposed to be derived from the Peruvian words Anta, or tapir; Anti, meaning metal or copper; and Ant-is, the name of a tribe resident in the mountains; or from the Spanish Andenes, applied to the gardens on the terraces which occur on the western slopes of the Andes in Chili. Humboldt believes its meaning has been lost. In connection with this may be noticed the curious fact mentioned by Colonel Tod, that the Hindoos of North India called the Himalayas by the name Andes.
The Andes form a continuous belt of mountainous high land along the western margin of South America, and have been considered by many writers as the southern continuation of the Rocky Mountains, which form a similar belt along the west side of North America. There are many objections against this view, and in favour of that which makes the Andes and Rocky Mountains two distinct ranges. In New Granada, or Columbia, as it is now called, the eastern range of the Andes terminates on the western side of the Gulf of Maracaybo, near 72 W. long. South of the gulf a branch range is thrown off, which traverses Venezuela, The central range dies out in the low lands south of the junction of the Cauca and Magdalena rivers. The western range also lowers and spreads in breadth in advancing northwards, and is lost in the low flats along the south margin of the Gulf of Darien. At the neck of the Panama isthmus, the Naipi and Cupica valleys stretch from the Atlantic to the Pacific Ocean, and are nowhere more than a few hundred feet above the level of the sea. North of the Atrato a serpentine ridge of mountains occurs, which terminates in Cape Tiburon. It is crossed by a pass called Tanela, which is about 5 miles in length, and 130 feet above the sea. Most of the isthmus between 8 and 9 N. lat. is below the level of this pass. Here the Isthmus of Panama curves round westwardly; and west of Panama there is another broad low tract stretching right across. This district cannot be regarded as belong ing in any way to the Andes. In Central America the mountains form numerous isolated ranges. In Mexico there are two high sierras. The eastern sierra does not reach the Rio Branco. The western sierra terminates at its north end in the Sierra Madre de Durango, which dies out in the northern part of Chihuahua and in Sonora, without being in any way connected with the Rocky Mountains.
The Rocky Mountains commence in about 100 W. long, at their south end, and terminate in about 145 W. at the north end, and have a general north-westerly direction. The Andes, on the other hand, commence near 54 S. lat. and 70 W. long. The southern portion forms a gentle curve, bending round to 73 W. in Patagonia, and reaching 70 again in the south of Chili. It continues on this line to Coquimbo, where it bends easterly, and after a slight double curve it cuts the meridian of 70 again south of Lake Titicaca. There is then a sharp bend, corresponding to that in the coast, which carries the range nearly to 80 W. in Ecuador, beyond which it again has an easterly bend, so as to cause it to terminate between 72 W. and 76 W. The north and south ends are consequently nearly in the same meridian. There are other dissimilarities between the Andes and the Rocky Mountains.
The formation of the Andes is due to several causes operating at distinct intervals of time. They consist mainly of stratified material which has been more or less altered. This material was deposited at the bottom of a sea, so that at some former time the highest portions were submerged, probably in consequence, to a certain extent, of subsidence of the sea bottom. Since the latest deposits there has been upheaval and denudation. The range, then, has resulted from the accumulation of sediment on a subsiding area ; from the subsequent upheaval of such deposits, which have been increased in height by the ejection of volcanic products; and from the operation of denuding agents.
probable that the Andes mark an area on which sedimentary deposits have been accumulated to a greater thickness than on any other portion of South America. It is further demonstrable that these deposits belong to several geological periods, the elevation having occurred at different periods, while their axes extend in different directions. Hence it is a complex range of mountains formed by the combination of several distinct systems of ridges. The width of the range varies from about 60 to 300 or more miles, biit, as compared with other mountains, the Andes are for the most part narrow relatively to their height. Where their special features are most characteristically developed, they consist of a massive embankment-like foundation, rising with a rapid slope from the low country on either side, and having its margins sitrmounted by lofty ridges of ragged or dome-like summits. These Cordilleras, as they are usually termed, flank longitudinal valleys, or plain-like depressions which form the highest levels of the central portion of the gigantic embankment, and which vary in width from 20 to 60 miles. At intervals the longitudinal depression is broken up, either by ridges connecting the Cordilleras, or by lofty plateau-like uplands. In several cases these transverse ridges and belts of high ground form the main watershed of the country. They are rarely cut across by the river systems, whereas both the marginal Cordilleras are intersected at numerous points, and more especially by the rivers draining the eastern slope of the country. In no case do these eastern rivers originate to the west of the western Cordilleras. A few of the central valleys, or plain-like depressions, have no connection either with the western or eastern river system. Roughly speak ing, the height of the central plains or valleys is from 6000 to 11,000 feet above the sea; of the passes and knots, from 10,000 to 15,000 feet; and of the highest peaks, from 18,000 to 23,290 feet the last being the altitude of Aconcagua in Cliili, which is generally considered to be the highest peak in America. Judging from these estimates, we may regard the bulk of the Andes as somewhere about that of a mass 4400 miles long, 100 miles wide, and 13,000 feet high, which is equivalent to 5,349,801,600,000,000 cubic feet. On this basis we find that the Mississippi would carry down an equivalent mass of matter in 785,000 years. The rate of denudation in certain river basins varies from one foot in 700 years, to one foot in 12,000 years. Assuming that similar rates would apply to the Andes, they would be denuded away in from 9 to 156 million years. In all probability, much less than 9 million years would suffice. On the other hand, the Andes would be swept away in 135,000 years, supposing the denuding powers of the globe were concentrated on them alone. From the above data, and assuming the average specific gravity of the matter forming the Andes to be 2 5, the weight of the portion above the sea may be estimated at 368,951,834,482,750 tons, giving an average of about 1000 tons on each square foot at the level of the sea. Under Aconcagua the pressure would be about 1780 tons per square foot at the same level, provided, of course, it were not, as it no doubt is, more or less modified by lateral pressure. These figures afford some, though at best a vague, conception of the mighty grandeur of this range of mountains, and of the scope there is for the exertion of enormous pressure. How vast, then, must be those forces which have counteracted such pressures, and upheaved the ocean-spread sediments of the continent, until the Andes, that— " giant of tlie "Western Star, Looks from his throne of clouds O er half the world ! But, however vast the Andes may seem to us, it should be remembered that they form but an insignificant portion of the globe itself. Aconcagua is about 3roVir tn f ^ e earth s diameter, which is relatively not more than apimple -g^th. of an inch high on the skin of a tall man.
south with Cape Horn, although for several degrees it is much broken up by arms and straits of the sea. The first portion of any extent commences between Cape Good Success and Cape San Paulo, and stretches across Tierra del Fuego, by Mount Darwin and Mount Sarmiento, and the range of hills on either side of Admiralty Sound. The mountains named are from 6600 to 6800 feet high. The Strait of Magellan also cuts through and across the range, isolating the mountainous islands of Clarence and Santa Ines. Otway Water cuts through the range, and pene trates to the plain of Patagonia. North of this are several snowy eminences, and in some places glaciers descend almost to the sea-level. At Last Hope Inlet, or a little north of 52 S., we have the commencement of the Andes as a continuous range, Disappointment Bay being the most northern place where the Pacific reaches the plains to the east of the Andes. South of this, and for several degrees to the north, the islands which fringe the coast have a mountainous character, and appear to belong essentially to the Andes range, with which there is reason to believe they were once connected. Along this space the Andes en croach upon the ocean, and have no western slope proper. Many of the sea channels are very narrow and ravine-like in character; they appear to represent a valley between two ridges of mountains, a feature which is most con spicuous farther north. The highest part or crest of the range is close to the sea, and consequently the streams which fall into the Pacific are all small. Towards the south the width is about 20 miles; and in the latitude of Mount Stokes, which is 6400 feet high, it is 40 miles. North of this the range is in places more than 40 miles across. From 46 to 42 S., the mountains become some what higher, the loftier peaks ranging from 4000 to 8000 feet. Among the more conspicuous are Mount Yanteles, 8030 feet; Mount Melimoyu, 7500 feet; Mount Corcovado, 7510 feet; and Mount Minchinmadiva, 7406 feet above the sea-level. The Eyre Sound glaciers descend to the sea- level. At about 41 30 S. lat. there is a low pass across the Andes; and to the north of this the slope is more or less distant from the sea, except, perhaps, at one part where the desert of Atacama terminates in lofty cliffs on the shore. In Chili the Andes increase in height and width, and between about 38 and 28 S. run approximately north and south; and nowhere do they recede so far from the sea as in the southern part of Chili. At this part, or in about the latitude of Antuco (36 50 S.), the lower land on the west is more than 100 miles broad, and the width of the range itself is probably more than 100 miles. Here the Andes consist of two ranges, the crests of which are from 60 to 80 miles apart, enclosing a longitudinal valley. Across these ranges there is a pass, which, with the excep tion of those near the mountains Osorno and Villarica, is the most southern in Chili. The summit of this pass is not more than 12,000 feet above the sea. The pass of Planchon lies north of Mount Dcscabezado; and to the south of Peteroa is the pass of Las Damas, which is pro bably not more than 11,000 feet at its highest point. At the head of the Maypu valley a pass traverses the two ranges of the Andes as well as the included valley of Tunuyan. That through the western range is called Peu- quenes Pass, and rises to 13,210 feet above the sea-level; while that through the eastern range is called Portillo, and rises to 14,365 feet above the sea. Near 32 38 S., Aconcagua rises to 23,290 feet, and is, so far as known, the highest peak in America, and the highest volcano in the world. A little to the south of it is the Cunibre or Uspallata Pass. In the western range it rises to 12,454 feet above the sea; and on its north flank is the pass of Los Patos. At about 30 S. the mountainous system becomes more complicated, owing to the appearance of several ranges which rise out of the plains towards the north-west corner of the Argentine Confederation, some of which run north and join the lofty highlands of the Bolivian Andes. It is doubtful whether all strictly belong to the Andes. Thus, in the latitude of Coquimbo, where both the mountains and the coast line trend somewhat to the east of north, there are three parallel mountain ranges. The western is called the Andes, the central range is known as the Sierra Famatina, and the eastern as the Sierra Velasco. The two latter ranges are quite isolated from the first-mentioned range, terminating abruptly on the north and south. North of 28 S., however, a number of sierras which rise from the Argentine plain form an extensive mass of mountains. These are continuous into the Cordilleras de los Valles, de Despoblado, and Abra de Cortaderas, which form the eastern margin of the lofty mountain plains of Bolivia. These plains slope down from the eastern side of the Andes, just as the Atacama desert seems to form part of the western slope. At about 22 S. the Andes begin to trend somewhat to the west of north. At about 20 S. the eastern and western ranges are connected by a lofty transverse chain about 60 miles broad, and similar to the mountain knots of Peru. North of this the ranges bend more to the west, and enclose the extensive valley of the Desaguadero river and Lake Titicaca, which is shut in on the north by the transverse chain of the Vilcanota Moun tains. The width of the range is in this part from 200 to 250 miles; or if the offset running eastward to Santa Cruz be included, the width is between 500 and 600 miles. One special feature about this part of the range is, that the Desaguadero valley (13,000 feet above the sea) is the largest in the Andes which has no connection with the river systems on the outer flanks, whether to the east or to the west. There are one or two small ones of a similar kind in the north-west part of the Argentine Confederation. The highlands which surround this great valley (which might be appropriately called the navel of South America) form a continuous re-entering watershed, separating respectively the numerous small rivers flowing into the Pacific, the Amazon system, Avhich drains a large portion of the northern part of South America, and the La Plata system, which drains most of the southern part of the same area. In this region, too, more especially in the eastern Cordillera, it was for a time believed, on the authority of Mr Pentland, that the highest peaks of the Andes were situated; his first estimates were, however, ascertained by himself and others to have been too great. The highest peak is the Nevado de Sorata, close to Lake Titicaca, and estimated at 21,286 feet high; next to it comes the twin peaked Illimani, a little further south, which rises to 21,181 feet. The passes crossing the valley have summits averaging 14,000 feet, but the one which skirts the Nevado do Sorata rises nearly to 16,000 feet above the sea, From about 18 the Andes, like the coast, runs north-west, so that whereas in about 18 S. the crest of the western Cordillera is in 70 W. long., at. 14 S. it has reached a little beyond 75. Here there is another change of direction, this portion of the western Cordillera stretching from about 14 S. to 6 S., the south end being near 75 W., and the north near 80 W., the westing being rather more than half a degree per degree of latitude. From 6 S. to the equator the direction is very slightly to the east of north; beyond this the trend is still more east, so that the termination of the west Cordillera lies between 76 and 78 W. long, in between 7 and 8 N. lat. The northern end of the eastern Cordillera is near 72 W. Returning again, to the Peru vian Andes, we find some lofty peaks which rival, and it may be surpass, those of Bolivia, Thus Sehama is reputed to be 22,000 feet; Chungara somewhat less; Chipicani, 18,898 feet; Arequipa, 18,373; Chuquibamba, 21,000 feet. There are numerous passes over the Andes in Peru, such as those of Gualillos, of the Altos de los Huescos, and of the Altos de Toledo the first mentioned of which rise to 17,820 feet above the sea. North of the Vilcanota Mountains the eastern portion of the Andes is much cut up by the numerous feeders of the Ucayali and Madeira rivers, most of which originate on the flanks of the western Cordillera. At Pasco there is a lofty mountain knot or table-land, which connects the Cordilleras, and at the same time forms the watershed between the upper portions of the basins of the rivers Ucayali, Huallaga, and the Maranon, or Upper Amazon. From this table-land three Cordilleras extend northward, of which the eastern dies out between the Ucayali and Huallaga rivers; the central between the Huallaga and the Upper Amazon; while the western Cordillera is continuous into the mountain knot of Loja, which forms the southern portion of the Andes of Ecuador, and which is estimated to be 11,650 square miles in extent. From this knot two lofty Cordilleras, abounding in volcanoes, both active and extinct, run nearly parallel. They are separated at intervals by transverse ridges into three vast mountain valley plains, of which the two southernmost drain into the Amazon basin, and the northernmost into the basin of the Esmeraldas river. The two Cordilleras are again united in the north by the mountain knot of Los Pastos, on the borders of Ecuador and Columbia. The valley plains are about 40 miles wide. On the south is the valley of Cuenca, which is about 50 miles long, and about 7800 feet above the sea. From it the way into the central valley plain, that of Ambato, is across the transverse ridge by the pass of Assuay, which rises to 15,520 feet, it is about 130 miles long, and about 8000 feet above the sea. The mountain fringe comprises several important volcanoes, viz., Sangay, Tunguragua, and Cotopaxi in the eastern Cordillera ; and the volcano Carguirazo in the western Cordillera, which also includes the lofty Chimborazo, estimated to reach 21,424 feet above the sea. Then crossing over the low transverse ridge of the Alto de Chisinche, we descend into the valley-plain of Quito, which is bordered by one of the most intensely volcanic areas on the globe. To the east are Sinchulagua, Antisana, and Cayambe ; the last is now extinct, stands on the equator, and is 19,534 feet above the sea. It is the highest point on the equator in the globe, and is the only one along that line where perpetual snow exists. In the western Cordillera the prominent eminences are Pichincha and Irnbabura. The valley-plain is about 9500 feet above the sea. Taking Cotopaxi as a centre, Orton observes that the other peaks may be arranged in concentric orbits thus. Runiinaqui and Sinchulagua are 10 miles distant; Iliniza, Corazon, Atacatzo, and Antisana are 25 miles ; Quirotoa, Pichin cha, and Guamani are 30 miles; Llanganati is 40 miles; Tunguragua, Carguirazo, Cayambi, are 50 miles; Chimborazo, Imbabura, and Cotocachi, are 60 miles; Altar is 65 miles; Sangay is 75 miles; lastly, Chiles and Assuay are 100 miles. Chimborazo is the most conspicuous feature in this part of the Andes, and from one point its outline resembles that of a lion at rest, Cotopaxi is the most symmetrical active volcano on the globe. Its apical angle is 122 30 ; and the slope is a little over 30 on the south, west, and east sides, and nearly 27 on the north side. Its summit was attained for the first time on November 27, 1872, by Drs Reiss and Stiibel. The height was found to be about 19,500 feet. Beyond the mountain knot of Los Pastos two Cordilleras run in a north-easterly direction to about 2 N. The western Cordillera is broken by the valley of the Patia, which has its source on the slopes of the valley between the mountain knot of Los Pastos and the transverse ridge south of Popayan. The eastern Cordillera is continued into the Paramo de Guanacas, from which basis the Andes spread out fan-like into three Cordilleras. This paramo, like the cross range between Iliniza and Cotopaxi, forms part of the main watershed between the rivers draining into the Atlantic and Pacific Oceans. North of the paramo this watershed runs along the western Cordillera for some distance, and then crosses several minor ranges of hills with their intervening valleys. The low watersheds at the head of the Atrato basin coincide with it; and north of Cupica Bay it suddenly bends, pass ing from within a few miles of the Pacific to within a few miles of the Atlantic Ocean. Having commenced this general account of the Andes with a notice of the mountain ranges of Columbia, and of the lowlands of the Isthmus of Panama, we thus come round to our starting- point. In the article America there is a brief account of the chain from a geological point of view, as well as of the transverse chains of South America; and under the heads of the various countries through which these passfurther particulars are given.
wishes to enter more minutely into this subject: Hum- boldt s works on South America; his papers in the Journal de Physique, vol. liii. p. 30 (1801); another in Gilbert s Annalen, vol. xvi. pp. 394, 450 (1804); Pentland s papers in Phil. Mag., vol. ix. p. 115 (1828), and in the Journal of the Roy. Geoy. Soc., vol. v. p. 30 (1835); papers by Pissis in Comptes Rendus, vol. xl. p. 764 (1855), and vol. lii. p. 1147 (1861), as also in Annales dcs Mines, fifth series, vol. ix. p. 81 (1856); D. Forbes, "On the Geology ofBolivia and South Peru" in Q. Jour. Geol. Soc., vol. xvii. p. 7; Rammelsberg in Monatsbericht Akad. Wiss., Berlin, p. 326 (1870); Orton, The Andes and the Amazon (1870); Rickard, A Mining Journey Across the Andes (1863); Cunningham (R. O.), Natural History of the Strait of Magellan (1871).