PHYSICAL HISTORY OF THE AMAZOXS. 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 



