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 



