glossy green of the foliage, but above all the general luxuriance of
the vegetation, filled me with admiration. A most paradoxical mixture
of sound and silence pervades the shady parts of the wood. The noise
from the insects is so loud, that it may be heard even in a vessel
anchored several hundred yards from the shore; yet within the recesses
of the forest a universal silence appears to reign. To a person fond
of natural history, such a day as this brings with it a deeper pleasure
than he can ever hope to experience again. After wandering about for
some hours, I returned to the landing-place; but, before reaching it, I
was overtaken by a tropical storm. I tried to find shelter under a
tree, which was so thick that it would never have been penetrated by
common English rain; but here, in a couple of minutes, a little torrent
flowed down the trunk. It is to this violence of the rain that we must
attribute the verdure at the bottom of the thickest woods: if the
showers were like those of a colder climate, the greater part would be
absorbed or evaporated before it reached the ground. I will not at
present attempt to describe the gaudy scenery of this noble bay,
because, in our homeward voyage, we called here a second time, and I
shall then have occasion to remark on it.
Along the whole coast of Brazil, for a length of at least 2000 miles,
and certainly for a considerable space inland, wherever solid rock
occurs, it belongs to a granitic formation. The circumstance of this
enormous area being constituted of materials which most geologists
believe to have been crystallized when heated under pressure, gives
rise to many curious reflections. Was this effect produced beneath the
depths of a profound ocean? or did a covering of strata formerly extend
over it, which has since been removed? Can we believe that any power,
acting for a time short of infinity, could have denuded the granite
over so many thousand square leagues?
On a point not far from the city, where a rivulet entered the sea, I
observed a fact connected with a subject discussed by Humboldt. [7] At
the cataracts of the great rivers Orinoco, Nile, and Congo, the
syenitic rocks are coated by a black substance, appearing as if they
had been polished with plumbago. The layer is of extreme thinness; and
on analysis by Berzelius it was found to consist of the oxides of
manganese and iron. In the Orinoco it occurs on the rocks periodically
washed by the floods, and in those parts alone where the stream is
rapid; or, as the Indians say, "the rocks are black where the waters
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