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---continuation commentary
#37b----
Under this layer of red
soil is rock of fairly loose foliaceous granite; most of all the feldspar it contains is such that it can be held
between your  fingers, while the other components, quartz and mica, are
fairly small and fragmented, though not altogether pulverized into another
form. The feldspar, to the contrary, has changed into Caolin
or porcellaneous earth. You will discern now some large crystals of
feldspar changed into that form, and now veins of it several finger lengths
wide snaking through the rock in different paths. These things being so,
you would not be wrong to infer or assert that the red clay mixed with iron and full of flint and mica, which throughout much of the province
of Rio de Janeiro makes up the soil in which those magnificent forests grow, arose from
foliaceous granite that was loosened in that way; the moisture of the
air, which is saturated with a large amount of carbonic acid, plays the
principle role in this change.(1)
Therefore it is perfectly understandable
that rocks of such composition, which are well-accommodated to healthy
plant life if they are continuously transformed by abundant moisture from
the air and dissolved with little difficulty, nourish the luxurious growth
of the forests that we admire in those mountains; in addition to this
comes nature's foresight, which made the forest itself its own nourisher
by attracting rains and drawing them into its shadows. In fact a deeper
layer of soil is not needed, as we already mentioned above, so long as
the forest remains untouched; indeed the forest itself contributes most
of all to the dissolution of the soil and thereby procures its own nourishment.
But where the ground has been laid bare
across extensive stretches, especially where a mad fury runs riot with
steel and fire from the tops of mountains down to their roots, plant life
struggles very much. For in those places where less moisture is drawn
from the air or retained, and where the water is able to linger only briefly
and cannot sink into the ground, there the primeval forest is not regenerated:
then only that form of forest comes forth which is called Capoeira among the inhabitants. (See etching #6) If such
a cutting were repeated across the mountain-sides, the ground itself would
become utterly feeble and finally a barren dryness would ensue, such as Palestine, Greece and other
lands which long ago flourished with rich cultivation.
 
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