CHAPTER IX, 
RIVERS.’ 
I HAVE had occasion oftener than once in giving pre- 
ceding details to make mention of the circumstance that 
many of the forests in Norway, and more especially the 
forests of broad-leaved trees, are situated in river basins, 
lining the river bed. In South Africa I have often seen 
that from some little eminence, whence the traveller could 
survey an extensive plain, one could trace the venation of 
it by river beds by the well-marked line of trees upon the 
banks; and I find a similar appearance is presented by 
the forest maps of several divisions of Norway. 
It is on moisture in the atmosphere derived from the 
sea to a great extent by evaporation on which vegetation 
depends. Even when sustained in solution, and invisible, 
this is absorbed by the soil, which has a great affinity for it. 
The power of the air to sustain water in solution varies 
with varying temperature ; and a fall in temperature may 
occasion a deposit of the surplus beyond what can be 
sustained, which deposit may, according to circumstances, 
take the form of cloud, of mist, of dew, of rain, of snow, or 
of hail. The soil, also, can only retain-a definite quantity 
of moisture, varying with its constituents, and the excess 
which may reach it at any time passes off in streamlets, 
brooks, and rivers. In this respect the rain and the 
river are alike—they are the drainage off of water in 
excess; but in this also they are alike—they may convey 
moisture from where it is not required to some other 
place where it may be utilised in the promotion of vege- 
tation, And all along a river from its rise to its flow into 
the sea, the reservoir of the world, the banks to a 
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