The Cordillera of the Andes, considered in its whole extent, from the rocky wall of the island of Diego Ramirez to the isthmus of Panama, is sometimes ramified into chains more or less parallel, and sometimes articulated by immense knots of mountains. We distinguish nine of those knots, and consequently an equal number of branching-points and ramifications. The latter are generally bifurcations. The Andes are twice only divided into three chains; in the knot of Huanuco, near the source of the Amazon, and the Huallaga (latitude 10 to 11 degrees) and in the knot of the Paramo de las Papas (latitude 2 degrees), near the source of the Magdalena and the Cauca. Basins, almost shut in at their extremities, parallel with the axis of the Cordillera and bounded by two knots and two lateral chains, are characteristic features of the structure of the Andes. Among these knots of mountains some, for instance those of Cuzco, Loxa and Los Pastos, comprise 3300, 1500 and 1130 square leagues, while others no less important in the eye of the geologist are confined to ridges or transversal dykes. To the latter belong the Altos de Chisinche (latitude 0 degrees 40 minutes south) and the Los Robles (latitude 2 degrees 20 minutes north), on the south of Quito and Popayan. The knot of Cuzco, so celebrated in the annals of Peruvian civilization, presents an average height of from 1200 to 1400 toises, and a surface nearly three times greater than the whole of Switzerland. The ridge of Chisinche, which separates the basins of Tacunga and Quito, is 1580 toises high, but scarcely a mile broad. The knots or groups which unite several partial chains have not the highest summits, either in the Andes or, for the most part, in the great mountain ranges of the old continent; it is not even certain that there is always in those knots a widening of the chain. The greatness of the mass, and the height so long attributed to points whence several considerable branches issue, was founded either on theoretic ideas or on false measures. The Cordilleras were compared to rivers that swell as they receive a number of tributary streams.
Among the basins which the Andes present, and which form probably as many lakes or small inland seas, those of Titicaca, Rio Jauja and the Upper Maranon, comprise respectively 3500, 1300, and 2400 square leagues of surface.* (* I here subjoin some measures interesting to geologists. Area of the Andes, from Tierra del Fuego to the Paramo de las Rosas (latitude 9 1/4 degrees north), where the mountainous land of Tocuyo and Barquesimeto begins, part of the Cordillera of the shore of Venezuela, 58,900 square leagues, (20 to a degree) the four spurs of Cordova, Salta, Cochabamba and Beni alone, occupy 23,300 square leagues of this surface, and the three basins contained between latitude 6 and 20 degrees south measure 7200 square leagues. Deducting 33,200 square leagues for the whole of the enclosed basins and spurs, we find, in latitude 65 degrees, the area of the Cordilleras elevated in the form of walls, to be 25,700 square leagues, whence results (comprehending the knots, and allowing for the inflexion of the chains) an average breadth of the Andes of 18 to 20 leagues. The valleys of Huallaga and the Rio Magdalena are not comprehended in these 58,900 square leagues, on account of the diverging direction of the chain, east of Cipoplaya and Santa Fe de Bogota.) The first is so encompassed that no drop of water can escape except by evaporation; it is like the enclosed valley of Mexico,* (* We consider it in its primitive state, without respect to the gap or cleft of the mountains, known by the name of Desaghue de Huehuetoca.) and of those numerous circular basins which have been discerned in the moon, and which are surrounded by lofty mountains. An immense alpine lake characterizes the basin of Tiahuanaco or Titicaca; this phenomenon is the more worthy of attention, as in South America there are scarcely any of those reservoirs of fresh water which are found at the foot of the European Alps, on the northern and southern slopes, and which are permanent during the season of drought. The other basins of the Andes, for instance, those of Jauja, the Upper Maranon and Cauca, pour their waters into natural canals, which may be considered as so many crevices situated either at one of the extremities of the basin, or on its banks, nearly in the middle of the lateral chain. I dwell on this articulated form of the Andes, on those knots or transverse ridges, because, in the continuation of the Andes called the Cordilleras of the shore of Venezuela, we shall find the same transverse dykes, and the same phenomena.
The ramification of the Andes and of all the great masses of mountains into several chains merits particular consideration in reference to the height more or less considerable of the bottom of the enclosed basins, or longitudinal valleys. Geologists have hitherto directed more attention to the successive narrowing of these basins, their depth compared with the walls of rock that surround them, and the correspondence between the re-entering and the salient angles, than to the level of the bottom of the valleys. No precise measure has yet fixed the absolute height of the three basins of Titicaca, Jauja and the Upper Maranon;* (* I am inclined to believe that the southern part of the basin of the Upper Maranon, between Huary and Huacarachuco, exceeds 350 toises.) but I was fortunate enough to be able to determine the six other basins, or longitudinal valleys, which succeed each other, as if by steps, towards the north. The bottom of the valley of Cuenca, between the knots of Loxa and Assuay, is 1350 toises; the valley of Allansi and of Hambato, between the knot of the Assuay and the ridge of Chisinche, 1320 toises; the valley of Quito in the eastern part, 1340 toises, and in the western part, 1490 toises; the basin of Almaguer, 1160 toises; the basin of the Rio Cauca, between the lofty plains of Cali, Buga, and Cartago, 500 toises; the valley of Magdalena, first between Neiva and Honda, 200 toises; and further on, between Honda and Mompox, 100 toises of average height above the level of the sea.* (* In the region of the Andes comprehended between 4 degrees of south latitude and 2 degrees of north, the longitudinal valleys or basins inclosed by parallel chains are regularly between 1200 and 1500 toises high; while the transversal valleys are remarkable for their depression, or rather the rapid lowering of their bottom. The valley of Patias, for instance, running from north-east to south-west is only 350 toises of absolute height, even above the junction of the Rio Guachion with the Quilquasi, according to the barometric measures of M. Caldas; and yet it is surrounded by the highest summits, the Paramos de Puntaurcu and Mamacondy. Going from the plains of Lombardy, and penetrating into the Alps of the Tyrol, by a line perpendicular to the axis of the chain, we advance more than 20 marine leagues towards the north, yet we find the bottom of the valley of the Adige and of Eysack near Botzen, to be only 182 toises of absolute height, an elevation which exceeds but 117 toises that of Milan. From Botzen however, to the ridge of Brenner (culminant point 746 toises) is only 11 leagues. The Valais is a longitudinal valley; and in a barometric measurement which I made very recently from Paris to Naples and Berlin, I was surprised to find that from Sion to Brigg, the bottom of the valley rises only to from 225 to 350 toises of absolute height; nearly the level of the plains of Switzerland, which, between the Alps and the Jura, are only from 274 to 300 toises.) In this region, which has been carefully measured, the different basins lower very sensibly from the equator northward. The elevation of the bottom of enclosed basins merits great attention in connection with the causes of the formation of the valleys. I do not deny that the depressions in the plains may be sometimes the effect of ancient pelagic currents, or slow erosions. I am inclined to believe that the transversal valleys, resembling crevices, have been widened by running waters; but these hypotheses of successive erosions cannot well be applied to the completely enclosed basins of Titicaca and Mexico. These basins, as well as those of Jauja, Cuenca and Almaguer, which lose their waters only by a lateral and narrow issue, owe their origin to a cause more instantaneous, more closely linked with the upheaving of the whole chain. It may be said that the phenomenon of the narrow declivities of the Sarenthal and of the valley of Eysack in the Tyrol, is repeated at every step, and on a grander scale, in the Cordilleras of equinoctial America. We seem to recognize in the Cordilleras those longitudinal sinkings, those rocky vaults, which, to use the expression of a great geologist,* "are broken when extended over a great space, and leave deep and almost perpendicular rents." (* Von Buch, Tableau du Tyrol meridional page 8 1823.)
If, to complete the sketch of the structure of the Andes from Tierra del Fuego to the northern Polar Sea, we pass the boundaries of South America, we find that the western Cordillera of New Grenada, after a great depression between the mouth of the Atrato and the gulf of Cupica, again rises in the isthmus of Panama to 80 or 100 toises high, augmenting towards the west, in the Cordilleras of Veragua and Salamanca,* and extending by Guatimala as far as the confines of Mexico. (* If it be true, as some navigators affirm, that the mountains at the north-western extremity of the republic of Columbia, known by the names of Silla de Veragua, and Castillo del Choco, be visible at 36 leagues distance, the elevation of their summits must be nearly 1400 toises, little lower than the Silla of Caracas.) Within this space it extends along the coast of the Pacific where, from the gulf of Nicoya to Soconusco (latitude 9 1/2 to 16 degrees) is found a long series of volcanoes,* most frequently insulated, and sometimes linked to spurs or lateral branches. (* See the list of twenty-one volcanoes of Guatimala, partly extinct and partly still burning, given by Arago and myself, in the Annuaire du Bureau des Longitudes pour 1824 page 175. No mountain of Guatimala having been hitherto measured, it is the more important to fix approximately the height of the Volcan de Agua, or the Volcano of Pacaya, and the Volcan de Fuego, called also Volcano of Guatimala. Mr. Juarros expressly says that this volcano which, by torrents of water and stones, destroyed, on the 11th September, 1541, the Ciudad Vieja, or Almolonga (the ancient capital of the country, which must not be confounded with the ancient Guatimala), is covered with snow, during several months of the year. This phenomenon would seem to indicate a height of more than 1750 toises.) Passing the isthmus of Tehuantepecor Huasacualco, on the Mexican territory, the Cordillera of central America extends on toward the intendancia of Oaxaca, at an equal distance from the two oceans; then from 18 1/2 to 21 degrees latitude, from Misteca to the mines of Zimapan, it approximates to the eastern coast. Nearly in the parallel of the city of Mexico, between Toluca, Xalapa and Cordoba, it attains its maximum height; several colossal summits rising to 2400 and 2770 toises. Farther north the chain called Sierra Madre runs north 40 degrees west towards San Miguel el Grande and Guanaxuato. Near the latter town (latitude 21 degrees 0 minutes 15 seconds) where the richest silver mines of the known world are situated, it widens in an extraordinary degree and separates into three branches. The most eastern branch advances towards Charcas and the Real de Catorce, and lowers progressively (turning to north-east) in the ancient kingdom of Leon, in the province of Cohahuila and Texas. That branch is prolonged from the Rio Colorado de Texas, crossing the Arkansas near the confluence of the Mississippi and the Missouri (latitude 38 degrees 51 minutes). In those countries it bears the name of the Mountains of Ozark,* and attains 300 toises of height. (* Ozark is at once the ancient name of Arkansas and of the tribe of Quawpaw Indians who inhabit the banks of that great river. The culminant point of the Mountains of Ozark is in latitude 37 1/2 degrees, between the sources of the White and Osage rivers.) It has been supposed that on the east of the Mississippi (latitude 44 to 46 degrees) the Wisconsin Hills, which stretch out to north-north-east in the direction of Lake Superior, may be a continuation of the mountains of Ozark. Their metallic wealth seems to denote that they are a prolongation of the eastern Cordillera of Mexico. The western branch or Cordillera occupies a part of the province of Guadalajara and stretches by Culiacan, Aripe and the auriferous lands of the Pimeria Alta and La Sonora, as far as the banks of the Rio Gila (latitude 33 to 34 degrees), one of the most ancient dwellings of the Aztek nations. We shall soon see that this western chain appears to be linked by the spurs that advance to the west, with the maritime Alps of California. Finally, the central Cordillera of Anahuac, which is the most elevated, runs first from south-east to north-west, by Zacatecas towards Durango, and afterwards from south to north, by Chihuahua, towards New Mexico. It takes successively the names of Sierra de Acha, Sierra de Los Mimbres, Sierra Verde, and Sierra de las Grullas, and about the 29 and 39 degrees of latitude, it is connected by spurs with two lateral chains, those of the Texas and La Sonora, which renders the separation of the chains more imperfect than the trifurcations of the Andes in South America.
That part of the Cordilleras of Mexico which is richest in silver beds and veins, is comprehended between the parallels of Oaxaca and Cosiquiriachi (latitude 16 1/2 to 29 degrees); the alluvial soil that contains disseminated gold extends some degrees still further northwards. It is a very striking phenomenon that the gold-washing of Cinaloa and Sonora, like that of Barbacoas and Choco on the south and north of the isthmus of Panama, is uniformly situated on the west of the central chain, on the descent opposite the Pacific. The traces of a still-burning volcanic fire which was no longer seen, on a length of 200 leagues, from Pasto and Popayan to the gulf of Nicoya (latitude 1 1/4 to 9 1/2 degrees), become very frequent on the western coast of Guatimala (latitude 9 1/2 to 16 degrees); these traces of fire again cease in the gneiss-granite mountains of Oaxaca, and re-appear, perhaps for the last time, towards the north, in the central Cordillera of Anahuac, between latitude 18 1/4 and 19 1/2 degrees, where the volcanoes of Taxtla, Orizaba, Popocatepetl, Toluca, Jorullo and Colima appear to be situated in a crevice* extending from east-south-east to west-north-west, from one ocean to the other. (* On this zone of volcanoes is the parallel of the greatest heights of New Spain. If the survey of Captain Basil Hall afford results alike certain in latitude and in longitude, the volcano of Colima is north of the parallel of Puerto de Navidad in latitude 19 degrees 36 minutes; and, like the volcano of Tuxtla, if not beyond the zone, at least beyond the average parallel of the volcanic fire of Mexico, which parallel seems to be between 18 degrees 59 minutes and 19 degrees 12 minutes.) This line of summits, several of which enter the limit of perpetual snow, and which are the loftiest of the Cordilleras from the peak of Tolima (latitude 40 degrees 46 minutes north), is almost perpendicular to the great axis of the chain of Guatimala and Anahuac, advancing to the 27th parallel, uniformly north 42 degrees east. A characteristic feature of every knot, or widening of the Cordilleras, is that the grouping of the summits is independent of the general direction of the axis. The backs of the mountains in New Spain form very elevated plains, along which carriages can roll for an extent of 400 leagues, from the capital to Santa-Fe and Taos, near the sources of Rio del Norte. This immense table-land, in 19 and 24 1/2 degrees, is constantly at the height of from 950 to 1200 toises, that is, at the elevation of the passes of the Great Saint Bernard and the Splugen. We find on the back of the Cordilleras of Anahuac, which lower progressively from the city of Mexico towards Taos, a succession of basins: they are separated by hills little striking to the eye of the traveller because they rise only from 250 to 400 toises above the surrounding plains. The basins are sometimes closed, like the valley of Tenochtitlan, where lie the great Alpine lakes, and sometimes they exhibit traces of ancient ejections, destitute of water.
Between latitude 33 and 38 degrees, the Rio del Norte forms, in its upper course, a great longitudinal valley; and the central chain seems here to be divided into several parallel ranges. This distribution continues northward, in the Rocky Mountains,* where, between the parallels of 37 and 41 degrees, several summits covered with eternal snow (Spanish Peak, James Peak and Big Horn) are from 1600 to 1870 toises of absolute height. (* The Rocky Mountains have been at different periods designated by the names of Chypewyan, Missouri, Columbian, Caous, Stony, Shining and Sandy Mountains.) Towards latitude 40 degrees south of the sources of the Paduca, a tributary of the Rio de la Plata, a branch known by the name of the Black Hills, detaches itself towards the north-east from the central chain. The Rocky Mountains at first seem to lower considerably in 46 and 48 degrees; and then rise to 48 and 49 degrees, where their tops are from 1200 to 1300 toises, and their ridge near 950 toises. Between the sources of the Missouri and the River Lewis, one of the tributaries of the Oregon or Columbia, the Cordilleras form in widening, an elbow resembling the knot of Cuzco. There, also, on the eastern declivity of the Rocky Mountains, is the partition of water between the Caribbean Sea and the Polar Sea. This point corresponds with those in the Andes of South America, at the spur of Cochabamba, on the east, latitude 19 degrees 20 minutes south; and in the Alto de los Robles (latitude 2 degrees 20 minutes north), on the west. The ridge that separates the Rocky Mountains extends from west to east, towards Lake Superior, between the basins of the Missouri and those of Lake Winnipeg and the Slave Lake. The central Cordillera of Mexico and the Rocky Mountains follow the direction north 10 degrees west, from latitude 25 to 38 degrees; the chain from that point to the Polar Sea prolongs in the direction north 24 degrees west, and ends in the parallel 69 degrees, at the mouth of the Mackenzie River.*
(* The eastern boundary of the Rocky Mountains lies:—
In 38 degrees latitude : 107 degrees 20 minutes longitude.
In 40 degrees latitude : 108 degrees 30 minutes longitude.
In 63 degrees latitude : 124 degrees 40 minutes longitude.
In 68 degrees latitude : 130 degrees 30 minutes longitude.)
In thus developing the structure of the Cordilleras of the Andes from 56 degrees south to beyond the Arctic circle, we see that its northern extremity (longitude 130 degrees 30 minutes) is nearly 61 degrees of longitude west of its southern extremity (longitude 60 degrees 40 minutes); this is the effect of the long-continued direction from south-east to north-west north of the isthmus of Panama. By the extraordinary breadth of the New Continent, in the 30 and 60 degrees north latitude, the Cordillera of the Andes, continually approaching nearer to the western coast in the southern hemisphere, is removed 400 leagues on the north from the source of the Rio de la Paz. The Andes of Chile may be considered as maritime Alps,* (* Geognostically speaking, a littoral chain is not a range of mountains forming of itself the coast; this name is extended to a chain separated from the coast by a narrow plain.) while, in their most northern continuation, the Rocky Mountains are a chain in the interior of a continent. There is, no doubt, between latitude 23 and 60 degrees from Cape Saint Lucas in California, to Alaska on the western coast of the Sea of Kamschatka, a real littoral Cordillera; but it forms a system of mountains almost entirely distinct from the Andes of Mexico and Canada. This system, which we shall call the Cordillera of California, or of New Albion, is linked between latitude 33 and 34 degrees with the Pimeria alta, and the western branch of the Cordilleras of Anahuac; and between latitude 45 and 53 degrees, with the Rocky Mountains, by transversal ridges and spurs that widen towards the east. Travellers who may at some future time pass over the unknown land between Cape Mendocino and the source of the Rio Colorado, may perhaps inform us whether the connexion of the maritime Alps of California or New Albion, with the western branch of the Cordilleras of Mexico, resembles that which, notwithstanding the depression, or rather total interruption observed on the west of the Rio Atrato, is admitted by geographers to exist between the mountains of the isthmus of Panama and the western branch of the Andes of New Grenada. The maritime Alps, in the peninsula of Old California, rise progressively towards the north in the Sierra of Santa Lucia (latitude 34 1/2 degrees), in the Sierra of San Marcos (latitude 37 to 38 degrees) and in the Snowy Mountains near Cape Mendocino (latitude 39 degrees 41 minutes); the last seem to attain at least the height of 1500 toises. From Cape Mendocino the chain follows the coast of the Pacific, but at the distance of from twenty to twenty-five leagues. Between the lofty summits of Mount Hood and Mount Saint Helen, in latitude 45 3/4 degrees, the chain is broken by the River Columbia. In New Hanover, New Cornwall and New Norfolk these rents of a rocky coast are repeated, these geologic phenomena of the fjords that characterize western Patagonia and Norway. At the point where the Cordillera turns towards the west (latitude 58 3/4 degrees, longitude 139 degrees 40 minutes) there are two volcanic peaks, one of which (Mount Saint Elias) perhaps equals Cotopaxi in height; the other (Fair-Weather Mountain) equals the height of Mount Rosa. The elevation of the former exceeds all the summits of the Cordilleras of Mexico and the Rocky Mountains, north of the parallel 19 1/4 degrees; it is even the culminant point in the northern hemisphere, of the whole known world north of 50 degrees of latitude. North-west of the peaks of Saint Elias and Fair-Weather the chain of California widens considerably in the interior of Russian America. Volcanoes multiply in number as we advance westward, in the peninsula of Alaska and the Fox Islands, where the volcano Ajagedan rises to the height of 1175 toises above the level of the sea. Thus the chain of the maritime Alps of California appears to be undermined by subterraneous fires at its two extremities; on the north in 60 degrees of latitude, and on the south, in 28 degrees, in the volcanoes of the Virgins.* (* Volcanes de las Virgenes. The highest summit of Old California, the Cerro de la Giganta (700 toises), appears to be also an extinguished volcano.) If it were certain that the mountains of California belong to the western branch of the Andes of Anahuac, it might be said that the volcanic fire, still burning, abandons the central Cordillera when it recedes from the coast, that is, from the volcano of Colima; and that the fire is borne on the north-west by the peninsula of Old California, Mount Saint Elias, and the peninsula of Alaska, towards the Aleutian Islands and Kamschatka.
I shall terminate this sketch of the structure of the Andes by recapitulating the principal features that characterize the Cordilleras, north-west of Darien.
Latitude 8 to 11 degrees. Mountains of the isthmus of Panama, Veragua and Costa Rica, slightly linked to the western chain of New Grenada, which is that of Choco.