12 BAHIA—BRAZIL. [cuap. 1. 
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 clime, 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 oceurs, it belongs to a granitic formation. The cir- 
cumstance 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.* 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 
* Pers, Narr., vol. v. pt. i. p..18. 
