The Low Lands of South America—Desert of Patagonia—The Pampas of Buenos
Ayres—The Silvas of the Amazons—The Llanos of the Orinoco and
Venezuela—Geological Notice.
THE southern plains are the most barren of the three great tracts of
American low lands; they stretch from Tierra del Fuego over 27 degrees
of latitude, or 1900 miles, nearly to Tucuman and the mountains of
Brazil. Palms grow at one end, deep snow covers the other many months in
the year. This enormous plain, of 1,620,000 square miles, begins on the
eastern part of Tierra del Fuego, which is a flat covered with trees,
and therefore superior to its continuation on the continent through
eastern Patagonia, which, for 800 miles from the land’s end to beyond
the Rio Colorado, is a desert of shingle.[52] It is occasionally
diversified by huge boulders, tufts of brown grass, low bushes armed
with spines, brine-lakes, incrustations of salt, white as snow, and by
black basaltic platforms, like plains of iron, at the foot of the Andes,
barren as the rest. Eastern Patagonia, however, is not one universal
flat, but a succession of shingly horizontal plains at higher and higher
levels, separated by long lines of cliffs or escarpments, the gable ends
of the tiers or plains. The ascent is small, for even at the foot of the
Andes the highest of these platforms is only 3000 feet above the ocean.
The plains are here and there intersected by a ravine or a stream, the
waters of which do not fertilize the blighted soil. The transition from
intense heat to intense cold is rapid, and piercing winds often rush in
hurricanes over these deserts, shunned even by the Indian, except when
he crosses them to visit the tombs of his fathers. The shingle ends a
few miles to the north of the Rio Colorado: there the red calcareous
earth of the Pampas begins, monotonously covered with coarse tufted
grass, without a tree or bush. This country, nearly as level as the sea
and without a stone, extends almost to the table-land of Brazil, and for
1000 miles between the Atlantic and the Andes, interrupted only at vast
distances by a solitary umbú, the only tree of this soil, rising like a
great landmark. This wide space, though almost destitute of water, is
not all of the same description. In the Pampas of Buenos Ayres there are
four distinct regions. For 180 miles west from Buenos Ayres they are
covered with thistles and lucern of the most vivid green so long as the
moisture from the rain lasts. In spring the verdure fades, and a month
afterwards the thistles shoot up 10 feet high, so dense and so protected
by spines that they are impenetrable. During the summer the dried stalks
are broken by the wind, and the lucern again spreads freshness over the
ground. The Pampas for 430 miles west of this region is a thicket of
long tufted luxuriant grass, intermixed with gaudy flowers, affording
inexhaustible pasture to thousands of horses and cattle; this is
followed by a tract of swamps and bogs, to which succeeds a region of
ravines and stones, and, lastly, a zone, reaching to the Andes, of
thorny bushes and dwarf trees in one dense thicket. The flat plains in
Entre Rios in Uruguay, those of Santa Fé, and a great part of Cordova
and Tucuman, are of sward, with cattle-farms. The banks of the Paraná,
and other tributaries of the La Plata, are adorned with an infinite
variety of tropical productions, especially the graceful tribe of palms;
and the river islands are bright with orange-groves. A desert of sand,
called El Gran Chaco, exists west of the Paraguay, the vegetable produce
of which is confined to a variety of the aloe and cactus tribes.
Adjoining this desert are the Bolivian provinces of Chiquitos and Moxos,
covered with forests and jungle, the scene of the most laborious and
benificent exertions of the Jesuit Missionaries towards the civilization
of the aborigines of South America in the last century.
The Pampas of Buenos Ayres, 1000 feet above the sea, sink to a low level
along the foot of the Andes, where the streams from the mountains
collect in large lakes, swamps, lagoons of prodigious size, and
wide-spreading salines. The swamp or lagoon of Ybera, of 1000 square
miles, is entirely covered with aquatic plants. These swamps are swollen
to thousands of square miles by the annual floods of the rivers, which
also inundate the Pampas, leaving a fertilizing coat of mud. Multitudes
of animals perish in the floods, and the drought that sometimes succeeds
is more fatal. Between the years 1830 and 1832 two millions of cattle
died from want of food. Millions of animals are sometimes destroyed by
casual and dreadful conflagrations in these countries when covered with
dry grass and thistles.[53]
The Silvas of the river of the Amazons, lying in the centre of the
continent, form the second division of the South American low lands.
This country is more uneven than the Pampas, and the vegetation is so
dense that it can only be penetrated by sailing up the river or its
tributaries. The forests not only cover the basin of the Amazons from
the Cordillera of Chiquitos to the mountains of Parima, but also its
limiting mountain-chains, the Sierra dos Vertentes and Parima, so that
the whole forms an area of woodland more than six times the size of
France, lying between the 18th parallel of south latitude and the 7th of
north; consequently inter-tropical and traversed by the equator. There
are some marshy savannahs between the 3d and 4th degrees of north
latitude, and some grassy steppes south of the Pacaraimo chain; but they
are insignificant compared with the Silvas, which extend 1500 miles
along the river, varying in breadth from 350 to 800 miles, and probably
more. According to Baron Humboldt, the soil, enriched for ages by the
spoils of the forest, consists of the richest mould. The heat is
suffocating in the deep and dark recesses of these primeval woods, where
not a breath of air penetrates, and where, after being drenched by the
periodical rains, the damp is so excessive that a blue mist rises in the
early morning among the huge stems of the trees, and envelops the
entangled creepers stretching from bough to bough. A death-like
stillness prevails from sunrise to sunset, then the thousands of animals
that inhabit these forests join in one loud discordant roar, not
continuous, but in bursts. The beasts seem to be periodically and
unanimously roused by some unknown impulse, till the forest rings in
universal uproar. Profound silence prevails at midnight, which is broken
at the dawn of morning by another general roar of the wild chorus.
Nightingales too have their fits of silence and song; after a pause they
“—— all burst forth in choral minstrelsy,
As if some sudden gale had swept at once
A hundred airy harps.” _Coleridge._
The whole forest often resounds when the animals, startled from their
sleep, scream in terror at the noise made by bands of its inhabitants
flying from some night-prowling foe. Their anxiety and terror before a
thunder-storm is excessive, and all nature seems to partake in the
dread. The tops of the lofty trees rustle ominously, though not a breath
of air agitates them; a hollow whistling in the high regions of the
atmosphere comes as a warning from the black floating vapour; midnight
darkness envelops the ancient forests, which soon after groan and creak
with the blast of the hurricane. The gloom is rendered still more
hideous by the vivid lightning and the stunning crash of thunder. Even
fishes are affected with the general consternation; for in a few minutes
the Amazons rages in waves like a stormy sea.
The Llanos of the Orinoco and Venezuela, covered with long grass, form
the third department of South American low lands, and occupy 153,000
square miles between the deltas of the Orinoco and the river Coqueta,
flat as the surface of the sea. It is possible to travel over these flat
plains for 1100 miles from the delta of the Orinoco to the foot of the
Andes of Pasto; frequently there is not an eminence a foot high in 270
square miles. They are twice as long as they are broad; and as the wind
blows constantly from the east, the climate is the more ardent the
farther west. These steppes for the most part are destitute of trees or
bushes, yet in some places they are dotted with the mauritia and other
palm-trees. Flat as these plains are, there are in some places two kinds
of inequalities; one consists of banks or shoals of grit or compact
limestone, five or six feet high, perfectly level for several leagues,
and imperceptible except on their edges: the other inequality can only
be detected by the barometer or levelling instruments; it is called a
Mesa, and is an eminence rising imperceptibly to the height of some
fathoms. Small as the elevation is, a mesa forms the watershed from S.W.
to N.E., between the affluents of the Orinoco and the streams flowing to
the northern coast of Terra Firma. In the wet season, from April to the
end of October, the tropical rains pour down in torrents, and hundreds
of square miles of the Llanos are inundated by the floods of the rivers.
The water is sometimes 12 feet deep in the hollows, in which so many
horses and other animals perish, that the ground smells of musk, an
odour peculiar to many South American quadrupeds. From the flatness of
the country too, the waters of some affluents of the Orinoco are driven
backwards by the floods of that river, especially when aided by the
wind, and form temporary lakes. When the waters subside, these steppes,
manured by the sediment, are mantled with verdure, and produce ananas,
with occasional groups of fan palm-trees, and mimosas skirt the rivers.
When the dry weather returns, the grass is burnt to powder; the air is
filled with dust raised by currents occasioned by difference of
temperature, even where there is no wind. If by any accident a spark of
fire falls on the scorched plains, a conflagration spreads from river to
river, destroying every animal, and leaves the clayey soil sterile for
years, till vicissitudes of weather crumble the brick-like surface into
earth.
The Llanos lie between the equator and the Tropic of Cancer; the mean
annual temperature is about 84° of Fahrenheit. The heat is most intense
during the rainy season, when tremendous thunder-storms are of common
occurrence.
GEOLOGY OF SOUTH AMERICA.
The most remarkable circumstance in the geological features of the South
American continent is the vast development of volcanic force, which is
confined to the chain of the Andes, and where it has acquired a
considerable breadth, as in the Peru-Bolivian portion, to the part
nearest the sea-coast. It would be wrong, however, to say that there are
no traces of modern volcanic action at a great distance from the
sea:[54] it is one of those theories which recent discoveries in both
continents have proved the fallacy of. The volcanic vents occur in the
Andes in linear groups: the most southern of these is that of Chile,
extending from the latitude of Chiloe to that of Santiago, 42° to 33°
S.: in this space exist five well-authenticated craters in ignition—the
most southern is the volcano of Llanquihae or Osorno, observed by M.
Gaye, and the most northern that of Maypu, the fires of which are
sometimes seen from the capital of Chile. Between the 32d parallel and
the Bolivian frontier there does not appear to be a single volcanic
vent, but in the province of Atacama rises the volcano of San Pedro of
Atacama. The mountain of Isluga, in the province of Tarapaca, is said to
be an active volcano, but the great centre of volcanic action in this
part of the Western Cordillera extends from 18° 10ʹ to 16° 20ʹ, where
the Andes have changed their direction from being parallel to the
meridian to one inclined nearly 45 degrees to that line. The trachytic
giant domes of the Andes, Sahama, and the Nevado of Chuquibamba mark the
N. and S. limits of this line of vents: the former, one of the most
perfect trachytic pyramids in the Andes, rises to a height of 22,350
feet, in lat. 18° 7ʹ and long. 68° 54ʹ W.; near to it are the twin
Nevados of Pomarape and Parinacota, one of which appears to emit smoke.
The group of snowy peaks seen from Arica, the centre of which, the
Nevado of Tacora, is in lat. 17° 43ʹ, offers a broken-down crater, and
an active solfaterra, on one of its sides. Between this point and the
volcano of Arequipa no active volcano has been observed. It is well
known that the latter has vomited flames and ashes, and spread
desolation around, at a comparatively recent period; the crater of
Uvinas, active in the 16th century, is now filled up and completely
extinct. Between the latitude of Arequipa (16° 24ʹ) and the Equatorial
group of volcanos, the Andes do not present a single active crater. This
Equatorial group extends over a meridional line of 3-1/4 degrees—between
the Peak of Sangay and the volcano of Los Pastos. The most remarkable of
these volcanic vents are the Sangay, Tunguragua, and Cotopaxi, all
situated in the Cordillera most remote from the ocean. Pichincha burned
as recently as 1831; and north of the Equator, Imbaburu, the volcanos of
Chiles, of Cumbal, of Tuqueres or Los Pastos, of Sotara and Purace, mark
the extension of actual volcanic action into our hemisphere.
Granite, which seems to be the base of the whole continent, is widely
spread to the east and south: it appears in Tierra del Fuego and in the
Patagonian Andes abundantly, and at great elevations, and in Chile and
southern Peru forms the line of hills parallel to the Pacific, and where
are situated the mineral riches of the former republic; but it comes
into view so rarely in the northern parts of the chain, that Baron
Humboldt says a person might travel years in the Andes of Peru and Quito
without falling in with it. He never saw it at a greater height above
the sea than 11,500 feet. Gneiss is here and there associated with the
granite, but micaschist is by much the most common of the crystalline
rocks. Quartz rock, probably of the Devonian period, is much developed,
generally mixed with mica, and rich in gold and specular iron. It
sometimes extends several leagues in the western declivities of Peru
6000 feet thick. Red sandstone, with its gypseous and saliferous marls,
of the age of our English red marl, of vast dimensions, occurs in the
Andes, and on the table-land east of them, where, in some places, as in
Colombia, it spreads over thousands of square miles to the shores of the
Atlantic. It is widely extended at altitudes of 10,000 and 12,000 feet—
for example, on the plains of Tarqui and in the valley of Cuença. Coal
is sometimes associated with it, and is found in the Andes of Pasco, in
Peru, 14,750 feet above the sea.
Porphyry abounds all over the Andes, from Patagonia to Colombia, at
every elevation, on the slopes and summits of the mountains rising to
the greatest elevation, but of very different ages and mineralogical
characters. One variety which frequently occurs is rich in metals, and
hence has been designated as _metalliferous_: in it are situated some of
the most celebrated silver mines of Peru, those of Potosi, Oruro, Puno.
The bare and precipitous porphyry-rocks give great variety to the
colouring of the Andes, especially in Chile, where purple, tile-red, and
brown are contrasted with the snow on the summit of the chain.[55]
Trachyte is almost as abundant as porphyry; many of the loftiest parts,
and all the great dome-shaped mountains, are formed of it. Masses of
this rock, from 14,000 to 18,000 feet thick, are seen on Chimborazo and
Pichincha. Prodigious quantities of volcanic products, lava, tufa, and
obsidian, occur on the western face of the Andes, where volcanos are
active. On the eastern side there are none. This is especially the case
in that part of the chain lying between the equator and Chile. The
Bolivian Cordilleras, which encircle the valley of Desaguadero, furnish
a striking example. The Cordillera of the coast is composed of
crystalline and stratified rocks at its base, and of trachytes,
obsidian, and trachytic conglomerates at greater elevations, while the
eastern Cordillera consists of stratified rocks of the Silurian system,
with granites, quartziferous porphyries, and syenites injected, and of
secondary rocks of the triassic period, and marls, containing gypsum,
oolitic limestone, and rock-salt of the most beautiful colours. Towards
Chile, and throughout the Chilian range, the case is different, because
active volcanos are there in the centre of the chain.
Sea-shells of different geological periods are found at various
elevations, which shows that many upheavings and subsidences have taken
place in the chain of the Andes.[56] The whole range, after twice
subsiding some thousand feet, was brought up by a slow movement in mass
during the Eiocene period, after which it sank down once more several
hundred feet, to be again uplifted to its present level by a slow and
often interrupted motion. These vicissitudes are very perceptible,
especially at its southern extremity. Stems of large trees, which Mr.
Darwin found in a fossil state in the Uspallata range, on the eastern
declivity of the Chilian Andes, now 700 miles distant from the Atlantic,
exhibit a remarkable example of such vicissitudes. These trees, with the
volcanic soil on which they had grown, had sunk from the beach to the
bottom of a deep ocean, from which, after five alternations of
sedimentary deposits and deluges of submarine lava of prodigious
thickness, the whole mass was raised up, and now forms the Uspallata
chain. Subsequently, by the wearing of streams, the embedded trunks have
been brought into view in a silicified state, projecting from the soil
in which they grew—now solid rock.
“Vast and scarcely comprehensible as such changes must ever appear, yet
they have all occurred within a period recent when compared with the
history of the Cordillera; and the Cordillera itself is absolutely
modern compared with many of the fossiliferous strata of Europe and
America.”[57]
From the quantity of shingle and sand in the valleys in the lower
ridges, as well as at altitudes from 7000 to 9000 feet above the present
level of the sea, it appears that the whole area of the Chilian Andes
has been rising for centuries by a gradual motion; and the coast is now
rising by the same imperceptible degrees, though it is sometimes
suddenly elevated by a succession of small upheavings of a few feet by
earthquakes, similar to that which shook the continent for 1000 miles on
the 20th of February, 1835.
On the eastern side of the Andes the land from Tierra del Fuego to the
Rio de la Plata has been raised _en masse_ by one great elevating force,
acting equally and imperceptibly for 2000 miles, within the period of
the shell-fish now existing, which, in many parts of these plains, even
still retain their colours. The gradual upward movement was interrupted
by at least eight long periods of rest, marked by the edges of the
successive plains, which, extending from south to north, had formed so
many lines of sea-coast, as they rose higher and higher between the
Atlantic and the Andes. It appears, from the shingle and fossil shells
found on both sides of the Cordillera, that the whole south-western
extremity of the continent has been rising slowly for a long time, and
indeed the whole Andean chain. The rise on the coast of Chile has been
at the rate of several feet in a century; but it has diminished
eastward, till, in the Patagonian plains and Pampas, it has been only a
few inches in the same line.
The instability of the southern part of the continent is less
astonishing, if it be considered that at the time of the earthquake of
1835 the volcanos in the Chilian Andes were in eruption
contemporaneously for 720 miles in one direction and 400 in another, so
that in all probability there was a subterranean lake of burning lava
below this end of the continent twice as large as the Black Sea.[58]
The terraced plains of Patagonia, which extend hundreds of miles along
the coast, are tertiary strata, not in basins, but in one great deposit,
above which lies a thick stratum of a white pumaceous substance,
extending at least 500 miles, a tenth part of which consists of marine
infusoria. Over the whole lies the shingle already mentioned, spread
over the coast for 700 miles in length, with a mean breadth of 200
miles, and 50 feet thick. These myriads of pebbles, chiefly of porphyry,
have been torn from the rocks of the Andes, and water-worn, at a period
subsequent to the deposition of the tertiary strata—a period of
incalculable duration. All the plains of Tierra del Fuego and Patagonia,
on both sides of the Andes, are strewed with huge boulders, which have
been supposed to have been transported by icebergs which had descended
to lower latitudes in ancient times than they do now—observations of
great interest, which we owe to Mr. Darwin.
The stunted vegetation of these sterile plains was sufficient to nourish
large animals of the pachydermata tribe, now extinct, even at a period
when the present shell-fish of the Patagonian seas existed.
The Pampas of Buenos Ayres are entirely alluvial, the deposit of the Rio
de la Plata. Granite prevails to the extent of 2000 miles along the
coast of Brazil, and with syenite forms the base of the table-land. The
superstructure of the latter consists of metamorphic and old igneous
rocks, sandstone, clay-slate, limestone, in which are large caverns with
bones of extinct animals, and alluvial soil. Gold is found in the
alluvial soil on the banks of the rivers, and diamonds, so abundant in
that country, in a ferruginous conglomerate of a very recent period.
The fertile soil of the Silvas has travelled from afar: washed down from
the Andes, it has been gradually deposited, and manured by the decay of
a thousand forests. Granite again appears, in more than its usual
ruggedness, in the table-land and mountains of the Parima system. The
sandstone of the Andes is found there also; and on the plains of
Esmeralda it caps the granite of the solitary prism-shaped Duida, the
culminating mountain of the Parima system. Limestone appears in the
Brigantine or Cocollar, the most southern of the three ranges of the
coast-chain of Venezuela; the other two are of granite, metamorphic
rocks, and crystalline schists, torn by earthquakes and worn by the sea,
which has deeply indented that coast. The chain of islands in the
Spanish main is merely the wreck of a more northern ridge, broken up
into detached masses by these irresistible powers.