Books: Equinoctial Regions of America V2

A >> Alexander von Humboldt >> Equinoctial Regions of America V2

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Farther south, towards Parapara and Ortiz, the slates disappear. They
are concealed under a trap-formation more varied in its aspect. The
soil becomes more fertile; the rocky masses alternate with strata of
clay, which appear to be produced by the decomposition of the
grunsteins, the amygdaloids, and the phonolites.

The grunstein, which farther north was less granulous, and passed into
serpentine, here assumes a very different character. It contains balls
of mandelstein, or amygdaloid, eight or ten inches in diameter. These
balls, sometimes a little flattened, are divided into concentric
layers: this is the effect of decomposition. Their nucleus is almost
as hard as basalt, and they are intermingled with little cavities,
owing to bubbles of gas, filled with green earth, and crystals of
pyroxene and mesotype. Their basis is greyish blue, rather soft, and
showing small white spots which, by the regular form they present, I
should conceive to be decomposed feldspar. M. von Buch examined with a
powerful lens the species we brought. He discovered that each crystal
of pyroxene, enveloped in the earthy mass, is separated from it by
fissures parallel to the sides of the crystal. These fissures seem to
be the effect of a contraction which the mass or basis of the
mandelstein has undergone. I sometimes saw these balls of mandelstein
arranged in strata, and separated from each other by beds of grunstein
of ten or fourteen inches thick; sometimes (and this situation is most
common) the balls of mandelstein, two or three feet in diameter, are
found in heaps, and form little mounts with rounded summits, like
spheroidal basalt. The clay which separates these amygdaloid
concretions arises from the decomposition of their crust. They acquire
by the contact of the air a very thin coating of yellow ochre.

South-west of the village of Parapara rises the little Cerro de
Flores, which is discerned from afar in the steppes. Almost at its
foot, and in the midst of the mandelstein tract we have just been
describing, a porphyritic phonolite, a mass of compact feldspar of a
greenish grey, or mountain-green, containing long crystals of vitreous
feldspar, appears exposed. It is the real porphyrschiefer of Werner;
and it would be difficult to distinguish, in a collection of stones,
the phonolite of Parapara from that of Bilin, in Bohemia. It does not,
however, here form rocks in grotesque shapes, but little hills covered
with tabular blocks, large plates extremely sonorous, translucid on
the edges, and wounding the hands when broken.

Such are the successions of rocks, which I described on the spot as I
progressively found them, from the lake of Tacarigua to the entrance
of the steppes. Few places in Europe display a geological arrangement
so well worthy of being studied. We saw there in succession six
formations: namely, mica-slate-gneiss, green transition-slate, black
transition-limestone, serpentine and grunstein, amygdaloid (with
pyroxene), and phonolite.

I must observe, in the first place, that the substance just described
under the name of grunstein, in every respect resembles that which
forms layers in the mica-slate of Cabo Blanco, and veins near Caracas.
It differs only by containing neither quartz, garnets, nor pyrites.
The close relations we observed near the Cerro de Chacao, between the
grunstein and the serpentine, cannot surprise these geologists who
have studied the mountains of Franconia and Silesia. Near Zobtenberg*
(* Between Tampadel and Silsterwiz.) a serpentine rock alternates also
with gabbro. In the district of Glatz the fissures of the gabbro are
filled with a steatite of a greenish white colour, and the rock which
was long thought to belong to the grunsteins* is a close mixture of
feldspar and diallage. (* In the mountains of Bareuth, in Franconia,
so abundant in grunstein and serpentine, these formations are not
connected together. The serpentine there belongs rather to the
schistose hornblende (hornblendschiefer), as in the island of Cuba.
Near Guanaxuato, in Mexico, I saw it alternating with syenite. These
phenomena of serpentine rocks forming layers in eurite (weisstein), in
schistose hornblende, in gabbro, and in syenite, are so much the more
remarkable, as the great mass of garnetiferous serpentines, which are
found in the mountains of gneiss and mica-slate, form little distinct
mounts, masses not covered by other formations. It is not the same in
the mixtures of serpentine and granulated limestone.)

The grunsteins of Tucutunemo, which we consider as constituting the
same formation as the serpentine rock, contain veins of malachite and
copper-pyrites. These same metalliferous combinations are found also
in Franconia, in the grunsteins of the mountains of Steben and
Lichtenberg. With respect to the green slates of Malpaso, which have
all the characters of transition-slates, they are identical with those
which M. von Buch has so well described, near Schonau, in Silesia.
They contain beds of grunstein, like the slates of the mountains of
Steben just mentioned.* (* On advancing into the adit for draining the
Friedrich-Wilhelmstollen mine, which I caused to be begun in 1794,
near Steben, and which is yet only 340 toises long, there have
successively been found, in the transition-slate subordinate strata of
pure and porphyritic grunstein, strata, of Lydian stone and ampelite
(alaunschiefer), and strata of fine-grained grunstein. All these
strata characterise the transition-slates.) The black limestone of the
Morros de San Juan is also a transition-limestone. It forms perhaps a
subordinate stratum in the slates of Malpaso. This situation would be
analogous to what is observed in several parts of Switzerland.* (* For
Instance, at the Glyshorn, at the Col de Balme, etc.) The slaty zone,
the centre of which is the ravine of Piedras Azules, appears divided
into two formations. On some points we think we observe one passing
into the other.

The grunsteins, which begin again to the south of these slates, appear
to me to differ little from those found north of the ravine of Piedras
Azules. I did not see there any pyroxene; but on the very spot I
recognized a number of crystals in the amygdaloid, which appears so
strongly linked to the grunstein that they alternate several times.

The geologist may consider his task as fulfilled when he has traced
with accuracy the positions of the diverse strata; and has pointed out
the analogies traceable between these positions and what has been
observed in other countries. But how can he avoid being tempted to go
back to the origin of so many different substances, and to inquire how
far the dominion of fire has extended in the mountains that bound the
great basin of the steppes? In researches on the position of rocks we
have generally to complain of not sufficiently perceiving the
connection between the masses, which we believe to be superimposed on
one another. Here the difficulty seems to arise from the too intimate
and too numerous relations observed in rocks that are thought not to
belong to the same family.

The phonolite (or leucostine compacte of Cordier) is pretty generally
regarded by all who have at once examined burning and extinguished
volcanoes, as a flow of lithoid lava. I found no real basalt or
dolerite; but the presence of pyroxene in the amygdaloid of Parapara
leaves little doubt of the igneous origin of those spheroidal masses,
fissured, and full of cavities. Balls of this amygdaloid are enclosed
in the grunstein; and this grunstein alternates on one side with a
green slate, on the other with the serpentine of Tucutunemo. Here,
then, is a connexion sufficiently close established between the
phonolites and the green slates, between the pyroxenic amygdaloids and
the serpentines containing copper-ores, between volcanic substances
and others that are included under the vague name of transition-traps.
All these masses are destitute of quartz like the real
trap-porphyries, or volcanic trachytes. This phenomenon is the more
remarkable, as the grunsteins which are called primitive almost always
contain quartz in Europe. The most general dip of the slates of
Piedras Azules, of the grunsteins of Parapara, and of the pyroxenic
amygdaloids embedded in strata of grunstein, does not follow the slope
of the ground from north to south, but is pretty regular towards the
north. The strata incline towards the chain of the coast, as
substances which had not been in fusion might be supposed to do. Can
we admit that so many alternating rocks, imbedded one in the other,
have a common origin? The nature of the phonolites, which are lithoid
lavas with a feldspar basis, and the nature of the green slates
intermixed with hornblende, oppose this opinion. In this state of
things we may choose between two solutions of the problem in question.
In one of these solutions the phonolite of the Cerro de Flores is to
be regarded as the sole volcanic production of the tract; and we are
forced to unite the pyroxenic amygdaloids with the rest of the
grunsteins, in one single formation, that which is so common in the
transition-mountains of Europe, considered hitherto as not volcanic.
In the other solution of the problem, the masses of phonolite,
amygdaloid, and grunstein, which are found in the south of the ravine
of Piedras Azules, are separated from the grunsteins and serpentine
rocks that cover the declivity of the mountains north of the ravine.
In the present state of knowledge I find difficulties almost equally
great in adopting either of these suppositions; but I have no doubt
that, when the real grunsteins (not the hornblende-grunsteins)
contained in the gneiss and mica-slates, shall have been more
attentively examined in other places; when the basalts (with pyroxene)
forming strata in primitive rocks* (* For instance, at Krobsdorf, in
Silesia, a stratum of basalt has been recognized in the mica-slate by
two celebrated geologists, MM. von Buch and Raumer. (Vom Granite des
Riesengebirges, 1813.) and the diabases and amygdaloids in the
transition mountains, shall have been carefully studied; when the
texture of the masses shall have been subjected to a kind of
mechanical analysis, and the hornblendes better distinguished from the
pyroxenes,* (* The grunsteins or diabases of the Fichtelgebirge, in
Franconia, which belong to the transition-slate, sometimes contain
pyroxenes.) and the grunsteins from the dolerites; a great number of
phenomena which now appear isolated and obscure, will be ranged under
general laws. The phonolite and other rocks of igneous origin at
Parapara are so much the more interesting, as they indicate ancient
eruptions in a granite zone; as they belong to the shore of the basin
of the steppes, as the basalts of Harutsh belong to the shore of the
desert of Sahara; and lastly, as they are the only rocks of the kind
we observed in the mountains of the Capitania-General of Caracas,
which are also destitute of trachytes or trap-porphyry, basalts, and
volcanic productions.* (* From the Rio Negro to the coasts of Cumana
and Caracas, to the east of the mountains of Merida, which we did not
visit.)

The southern declivity of the western chain is tolerably steep; the
steppes, according to my barometrical measurements, being a thousand
feet lower than the bottom of the basin of Aragua. From the extensive
table-land of the Villa de Cura we descended towards the banks of the
Rio Tucutunemo, which has hollowed for itself, in a serpentine rock, a
longitudinal valley running from east to west, at nearly the same
level as La Victoria. A transverse valley, lying generally north and
south, led us into the Llanos, by the villages of Parapara and Ortiz.
It grows very narrow in several parts. Basins, the bottoms of which
are perfectly horizontal, communicate together by narrow passes with
steep declivities. They were, no doubt, formerly small lakes, which,
owing to the accumulation of the waters, or some more violent
catastrophe, have broken down the dykes by which they were separated.
This phenomenon is found in both continents, wherever we examine the
longitudinal valleys forming the passages of the Andes, the Alps,* (*
For example, the road from the valley of Ursern to the Hospice of St.
Gothard, and thence to Airolo.) or the Pyrenees. It is probable, that
the irruption of the waters towards the Llanos have given, by
extraordinary rents, the form of ruins to the Morros of San Juan and
of San Sebastian. The volcanic tract of Parapara and Ortis is now only
30 or 40 toises above the Llanos. The eruptions consequently took
place at the lowest point of the granitic chain.

In the Mesa de Paja, in the ninth degree of latitude, we entered the
basin of the Llanos. The sun was almost at its zenith; the earth,
wherever it appeared sterile and destitute of vegetation, was at the
temperature of 48 or 50 degrees.* (* A thermometer, placed in the
sand, rose to 38.4 and 40 degrees Reaumur.) Not a breath of air was
felt at the height at which we were on our mules; yet, in the midst of
this apparent calm, whirls of dust incessantly arose, driven on by
those small currents of air which glide only over the surface of the
ground, and are occasioned by the difference of temperature between
the naked sand and the spots covered with grass. These sand-winds
augment the suffocating heat of the air. Every grain of quartz, hotter
than the surrounding air, radiates heat in every direction; and it is
difficult to observe the temperature of the atmosphere, owing to these
particles of sand striking against the bulb of the thermometer. All
around us the plains seemed to ascend to the sky, and the vast and
profound solitude appeared like an ocean covered with sea-weed.
According to the unequal mass of vapours diffused through the
atmosphere, and the variable decrement in the temperature of the
different strata of air, the horizon in some parts was clear and
distinct; in other parts it appeared undulating, sinuous, and as if
striped. The earth there was confounded with the sky. Through the dry
mist and strata of vapour the trunks of palm-trees were seen from
afar, stripped of their foliage and their verdant summits, and looking
like the masts of a ship descried upon the horizon.

There is something awful, as well as sad and gloomy, in the uniform
aspect of these steppes. Everything seems motionless; scarcely does a
small cloud, passing across the zenith, and denoting the approach of
the rainy season, cast its shadow on the earth. I know not whether the
first aspect of the Llanos excite less astonishment than that of the
chain of the Andes. Mountainous countries, whatever may be the
absolute elevation of the highest summits, have an analogous
physiognomy; but we accustom ourselves with difficulty to the view of
the Llanos of Venezuela and Casanare, to that of the Pampas of Buenos
Ayres and of Chaco, which recal to mind incessantly, and during
journeys of twenty or thirty days, the smooth surface of the ocean. I
had seen the plains or llanos of La Mancha in Spain, and the heaths
(ericeta) that extend from the extremity of Jutland, through Luneburg
and Westphalia, to Belgium. These last are really steppes, and, during
several ages, only small portions of them have yielded to cultivation;
but the plains of the west and north of Europe present only a feeble
image of the immense llanos of South America. It is in the south-east
of our continent, in Hungary, between the Danube and the Theiss; in
Russia, between the Borysthenes, the Don, and the Volga, that we find
those vast pastures, which seem to have been levelled by a long abode
of the waters, and which meet the horizon on every side. The plains of
Hungary, where I traversed them on the frontiers of Germany, between
Presburg and Oedenburg, strike the imagination of the traveller by the
constant mirage; but their greatest extent is more to the east,
between Czegled, Debreczin, and Tittel. There they present the
appearance of a vast ocean of verdure, having only two outlets, one
near Gran and Waitzen, the other between Belgrade and Widdin.

The different quarters of the world have been supposed to be
characterized by the remark, that Europe has its heaths, Asia its
steppes, Africa its deserts, and America its savannahs; but by this
distinction, contrasts are established that are not founded either on
the nature of things, or the genius of languages. The existence of a
heath always supposes an association of plants of the family of
ericae; the steppes of Asia are not everywhere covered with saline
plants; the savannahs of Venezuela furnish not only the gramina, but
with them small herbaceous mimosas, legumina, and other dicotyledonous
plants. The plains of Songaria, those which extend between the Don and
the Volga, and the puszta of Hungary, are real savannahs, pasturages
abounding in grasses;* (* These vast steppes of Hungary are elevated
only thirty or forty toises above the level of the sea, which is more
than eighty leagues distant from them. See Wahlenberg's Flora
Carpathianica. Baron Podmanitzky, an Hungarian nobleman, highly
distinguished for his knowledge of the physical sciences, caused the
level of these plains to be taken, to facilitate the formation of a
canal then projected between the Danube and the Theiss. He found the
line of division, or the convexity of the ground, which slopes on each
side towards the beds of the two rivers, to be only thirteen toises
above the height of the Danube. The widely extended pastures, which
reach in every direction to the horizon, are called in the country,
Puszta, and, over a distance of many leagues, are without any human
habitation. Plains of this kind, intermingled with marshes and sandy
tracts, are found on the western side of the Theiss, between Czegled,
Csaba, Komloss, and Szarwass; and on the eastern side, between
Debreczin, Karczag, and Szoboszlo. The area of these plains of the
interior basin of Hungary has been estimated, by a pretty accurate
calculation, to be between two thousand five hundred and three
thousand square leagues (twenty to a degree). Between Czegled,
Szolnok, and Ketskemet, the plain resembles a sea of sand.) while the
savannahs to the east and west of the Rocky Mountains and of New
Mexico produce chenopodiums containing carbonate and muriate of soda.
Asia has real deserts destitute of vegetation, in Arabia, in Gobi, and
in Persia. Since we have become better acquainted with the deserts in
the interior of Africa, so long and so vaguely confounded together
under the name of desert of Sahara (Zahra); it has been observed, that
in this continent, towards the east, savannahs and pastures are found,
as in Arabia, situated in the midst of naked and barren tracts. It is
these deserts, covered with gravel and destitute of plants, which are
almost entirely wanting in the New World. I saw them only in that part
of Peru, between Amotape and Coquimbo, on the shores of the Pacific.
These are called by the Spaniards, not llanos, but the desiertos of
Sechura and Atacamez. This solitary tract is not broad, but it is four
hundred and forty leagues long. The rock pierces everywhere through
the quicksands. No drop of rain ever falls on it; and, like the desert
of Sahara, north of Timbuctoo, the Peruvian desert affords, near
Huaura, a rich mine of native salt. Everywhere else, in the New World,
there are plains desert because not inhabited, but no real deserts.*
(* We are almost tempted, however, to give the name of desert to that
vast and sandy table-land of Brazil, the Campos dos Parecis, which
gives birth to the rivers Tapajos, Paraguay, and Madeira, and which
reaches the summit of the highest mountains. Almost destitute of
vegetation, it reminds us of Gobi, in Mongolia.)

The same phenomena are repeated in the most distant regions; and,
instead of designating those vast treeless plains in accordance with
the nature of the plants they produce, it seems natural to class them
into deserts, steppes, or savannahs; into bare lands without any
appearance of vegetation, and lands covered with gramina or small
plants of the dicotyledonous tribe. The savannahs of America,
especially those of the temperate zone, have in many works been
designated by the French term prairies; but this appears to me little
applicable to pastures which are often very dry, though covered with
grass of four or five feet in height. The Llanos and the Pampas of
South America are really steppes. They are covered with beautiful
verdure in the rainy season, but in the time of great drought they
assume the aspect of a desert. The grass is then reduced to powder;
the earth cracks; the alligators and the great serpents remain buried
in the dried mud, till awakened from their long lethargy by the first
showers of spring. These phenomena are observed on barren tracts of
fifty or sixty leagues in length, wherever the savannahs are not
traversed by rivers; for on the borders of rivulets, and around little
pools of stagnant water, the traveller finds at certain distances,
even during the period of the great droughts, thickets of mauritia, a
palm, the leaves of which spread out like a fan, and preserve a
brilliant verdure.

The steppes of Asia are all beyond the tropics, and form very elevated
table-lands. America also has savannahs of considerable extent on the
backs of the mountains of Mexico, Peru, and Quito; but its most
extensive steppes, the Llanos of Cumana, Caracas, and Meta, are little
raised above the level of the ocean, and all belong to the equinoctial
zone. These circumstances give them a peculiar character. They have
not, like the steppes of southern Asia, and the deserts of Persia,
those lakes without issue, those small systems of rivers which lose
themselves either in the sands, or by subterranean filtrations. The
Llanos of America incline to the east and south; and their running
waters are branches of the Orinoco.

The course of these rivers once led me to believe, that the plains
formed table-lands, raised at least from one hundred to one hundred
and fifty toises above the level of the ocean. I supposed that the
deserts of interior Africa were also at a considerable height; and
that they rose one above another as in tiers, from the coast to the
interior of the continent. No barometer has yet been carried into the
Sahara. With respect to the Llanos of America, I found by barometric
heights observed at Calabozo, at the Villa del Pao, and at the mouth
of the Meta, that their height is only forty or fifty toises above the
level of the sea. The fall of the rivers is extremely gentle, often
nearly imperceptible; and therefore the least wind, or the swelling of
the Orinoco, causes a reflux in those rivers that flow into it. The
Indians believe themselves to be descending during a whole day, when
navigating from the mouths of these rivers to their sources. The
descending waters are separated from those that flow back by a great
body of stagnant water, in which, the equilibrium being disturbed,
whirlpools are formed very dangerous for boats.

The chief characteristic of the savannahs or steppes of South America
is the absolute want of hills and inequalities--the perfect level of
every part of the soil. Accordingly the Spanish conquerors, who first
penetrated from Coro to the banks of the Apure, did not call them
deserts or savannahs, or meadows, but plains (llanos). Often within a
distance of thirty square leagues there is not an eminence of a foot
high. This resemblance to the surface of the sea strikes the
imagination most powerfully where the plains are altogether destitute
of palm-trees; and where the mountains of the shore and of the Orinoco
are so distant that they cannot be seen, as in the Mesa de Pavones. A
person would be tempted there to take the altitude of the sun with a
quadrant, if the horizon of the land were not constantly misty on
account of the variable effects of refraction. This equality of
surface is still more perfect in the meridian of Calabozo, than
towards the east, between Cari, La Villa del Pao, and Nueva Barcelona;
but it extends without interruption from the mouths of the Orinoco to
La Villa de Araure and to Ospinos, on a parallel of a hundred and
eighty leagues in length; and from San Carlos to the savannahs of
Caqueat, on a meridian of two hundred leagues. It particularly
characterises the New Continent, as it does the low steppes of Asia,
between the Borysthenes and the Volga, between the Irtish and the Obi.
The deserts of central Africa, of Arabia, Syria, and Persia, Gobi, and
Casna, present, on the contrary, many inequalities, ranges of hills,
ravines without water, and rocks which pierce the sands.

The Llanos, however, notwithstanding the apparent uniformity of their
surface, present two kinds of inequalities, which cannot escape the
observation of the traveller. The first is known by the name of banks
(bancos); they are in reality shoals in the basin of the steppes,
fractured strata of sandstone, or compact limestone, standing four or
five feet higher than the rest of the plain. These banks are sometimes
three or four leagues in length; they are entirely smooth, with a
horizontal surface; their existence is perceived only by examining
their margins. The second species of inequality can be recognised only
by geodesical or barometric levellings, or by the course of rivers. It
is called a mesa or table, and is composed of small flats, or rather
convex eminences, that rise insensibly to the height of a few toises.
Such are, towards the east, in the province of Cumana, on the north of
the Villa de la Merced and Candelaria, the Mesas of Amana, of Guanipa,
and of Jonoro, the direction of which is south-west and north-east;
and which, in spite of their inconsiderable elevation, divide the
waters between the Orinoco and the northern coast of Terra Firma. The
convexity of the savannah alone occasions this partition: we there
find the dividing of the waters (divortia aquarum* (* "C. Manlium
prope jugis [Tauri] ad divortia aquarum castra posuisse." Livy lib. 38
c. 75.)), as in Poland, where, far from the Carpathian mountains, the
plain itself divides the waters between the Baltic and the Black Sea.
Geographers, who suppose the existence of a chain of mountains
wherever there is a line of division, have not failed to mark one in
the maps, at the sources of the Rio Neveri, the Unare, the Guarapiche,
and the Pao. Thus the priests of Mongol race, according to ancient and
superstitious custom, erect oboes, or little mounds of stone, on every
point where the rivers flow in an opposite direction.