s to
powder by its action, would be deposited, and gradually transformed from
an unstratified paste containing the finest sand and mud, together with
coarse pebbles and gravel, into a regularly stratified formation. In
this formation the coarse materials would of course fall to the bottom,
while the most minute would settle above them. It is at this time and
under such circumstances that I believe the first formation of the
Amazonian Valley, with the coarse, pebbly sand beneath, and the finely
laminated clays above, to have been accumulated.

I shall perhaps be reminded here of my fossil leaves, and asked how any
vegetation would be possible under such circumstances. But it must be
remembered, that, in considering all these periods, we must allow for
immense lapses of time and for very gradual changes; that the close of
this first period would be very different from its beginning; and that a
rich vegetation springs on the very borders of the snow and ice fields
in Switzerland. The fact that these were accumulated in a glacial basin
would, indeed, at once account for the traces of vegetable life, and for
the absence, or at least the great scarcity, of animal remains in these
deposits. For while fruits may ripen and flowers bloom on the very edge
of the glaciers, it is also well known that the fresh-water lakes formed
by the melting of the ice are singularly deficient in life. There are
indeed hardly any animals to be found in glacial lakes.

The second formation belongs to a later period, when, the whole body of
ice being more or less disintegrated, the basin contained a larger
quantity of water. Beside that arising from the melting of the ice, this
immense valley bottom must have received, then as now, all which was
condensed from the atmosphere above, and poured into it in the form of
rain or dew. Thus an amount of water equal to that now flowing in from
all the tributaries of the main stream must have been rushing towards
the axis of the valley, seeking its natural level, but spreading over a
more extensive surface than now, until, finally gathered up as separate
rivers, it flowed in distinct beds. In its general movement toward the
central and lower part of the valley, the broad stream would carry along
all the materials small enough to be so transported, as well as those so
minute as to remain suspended in the waters. It would gradually deposit
them in the valley bottom in horizontal beds, more or less regular, or