PHYSICAL HISTORY OF THE AMAZONS. 429 
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 im- 
mense 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 vegeta- 
ble 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 at present. Thus an amount 
of water equal to that 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 
