In that part of the basin of the Orinoco
which runs in the direction of from south to north, as well as in that
running from west to east, the maxima of depression are found at the
foot of the Sierra Parime, we may even say, on its outline.
4. THE BASIN OF THE RIO NEGRO AND THE AMAZON.
This is the central and largest basin of South America. It is exposed
to frequent equatorial rains, and the hot and humid climate develops a
force of vegetation to which nothing in the two continents can be
compared. The central basin, bounded on the north by the Parime group,
and on the south by the mountains of Brazil, is entirely covered by
thick forests, while the two basins at the extremities of the
continent (the Llanos of Venezuela and the Lower Orinoco, and the
Pampas of Buenos Ayres or the Rio de la Plata) are savannahs or
prairies, plains without trees and covered with gramina. This
symmetric distribution of savannahs bounded by impenetrable forests,
must be connected with physical revolutions which have operated
simultaneously over great surfaces.
(4a.) PART OF THE BASIN OF THE AMAZON, RUNNING FROM EAST TO WEST,
BETWEEN 2 DEGREES NORTH AND 12 DEGREES SOUTH; 880 LEAGUES IN LENGTH.
The western shore of this basin is formed by the chain of the Andes,
from the knot of the mountains of Huanuco to the sources of the
Magdalena. It is enlarged by the spurs of the Rio Beni,* (* The real
name of this great river, respecting the course of which geographers
have been so long divided, is Uchaparu, probably water (para) of Ucha;
Peni also signifies river or water; for the language of the Maypures
has very many analogies with that of the Moxos; and veni (oueni)
signifies water in Maypure, as una in Moxo. Perhaps the river retained
the name of Maypure, after the Indians who spoke that language had
emigrated northward in the direction of the banks of the Orinoco.)
rich in gem-salt, and composed of several ranges of hills (latitude 8
degrees 11 minutes south) which advance into the plains on the eastern
bank of the Paro. These hills are transformed on our maps into Upper
Cordilleras and Andes of Cuchao. Towards the north the basin of the
Amazon, of which the area (244,000 square leagues) is only one-sixth
less than the area of all Europe, rises in a gentle slope towards the
Sierra Parime. At 68 degrees of west longitude the elevated part of
this Sierra terminates at 3 1/2 degrees north latitude. The group of
little mountains surrounding the source of the Rio Negro, the Inirida
and the Xie (latitude 2 degrees) the scattered rocks between the
Atabapo and the Cassiquiare, appear like groups of islands and rocks
in the middle of the plain. Some of those rocks are covered with signs
or symbolical sculpture. Nations, very different from those who now
inhabit the banks of the Cassiquiare, penetrated into the savannahs;
and the zone of painted rocks, extending more than 150 leagues in
breadth, bears traces of ancient civilization. On the east of the
sporadic groups of rocks (between the meridian of the bifurcation of
the Orinoco and that of the confluence of the Essequibo with the
Rupunuri) the lofty mountains of the Parime commence only in 3 degrees
north latitude; where the plains of the Amazon terminate.
The limits of the plains of the Amazon are still less known towards
the south than towards the north. The mountains that exceed 400 toises
of absolute height do not appear to extend in Brazil northward of the
parallels 14 or 15 degrees of south latitude, and west of the meridian
of 52 degrees; but it is not known how far the mountainous country
extends, if we may call by that name a territory bristled with hills
of one hundred or two hundred toises high. Between the Rio dos
Vertentes and the Rio de Tres Barras (tributary streams of the Araguay
and the Topayos) several ridges of the Monts Parecis run northward. On
the right bank of the Topayos a series of little hills advance as far
as the parallel of 5 degrees south latitude, to the fall (cachoeira)
of Maracana; while further west, in the Rio Madeira, the course of
which is nearly parallel with that of the Topayos, the rapids and
cataracts indicate no rocky ridges beyond the parallel of 8 degrees.
The principal depression of the basin of which we have just examined
the outline, is not near one of its banks, as in the basin of the
Lower Orinoco, but at the centre, where the great recipient of the
Amazon forms a longitudinal furrow inclining from west to east, under
an angle of at least 25 degrees. The barometric measurements which I
made at Javita on the banks of the Tuamini, at Vasivia on the banks of
the Cassiquiare and at the cataract of Rentema, in the Upper Maranon,
seem to prove that the rising of the Llanos of the Amazon northward
(at the foot of the Sierra Parime) is 150 toises, and westward (at the
foot of the Cordillera of the Andes of Loxa), 190 toises above the
sea-level.
(4b.) PART OF THE BASIN OF THE AMAZON STRETCHING FROM SOUTH TO NORTH.
This is the zone or land-strait by which, between 12 and 20 degrees of
south latitude, the plains of the Amazon communicate with the Pampas
of Buenos Ayres. The western bank of this zone is formed by the Andes,
between the knot of Porco and Potosi, and that of Huanuco and Pasco.
Part of the spurs of the Rio Beni, which is but a widening of the
Cordilleras of Apolobamba and Cuzco and the whole promontory of
Cochabamba, advance eastward into the plains of the Amazon.
