KIVERS. 



KIVERS. 



124. Formation of Rivers. The origin of all rivers is 

 the evaporation of the ocean. The surface of the oceans and 

 seas has an extent, as has been already explained, equal to 

 nearly three-fourths of the whole surface of the globe. This 

 extensive mass of water is subject to an incessant process of 

 evaporation. In this process, the pure water is separated from the 

 salt and other solid matter which it holds in solution. The vapour, 

 therefore, which ascends into and mixes with the atmosphere, is 

 that of pure fresh water. Being lighter bulk for bulk than the air, 

 it rises into the higher regions, where it is transported in different 

 directions by atmospheric currents. By the operation of tempera- 

 ture and electricity, it is converted into clouds, which, attracted 

 towards the most elevated points of the land, collect in dense 

 masses around the ridges and summits of the mountains, where, 

 being condensed and reconverted into water, and sometimes con- 

 gealed, it is precipitated in the form of rain or snow. From these 

 heights it descends by the common principle of gravitation, either 

 along the surface of the declivities, or through the fissures and 

 interstices of the soil, finding its way to the lower levels ; and, fol- 

 lowing these in their devious and winding course, it at length 

 returns to the sea, with which it mingles, to be again evapo- 

 rated and sent once more through the same series of physical 

 changes. 



125. Effect of a single ridge. When a tract of country, 

 bounded on either side by the sea, is traversed by an elevated 

 ridge or chain of mountains, the rain and snow deposited upon 

 them descends in streams along their slopes at either side, forming 

 at first rivulets, which, coalescing, swell into larger streams, and 

 acquire the character of rivers. These, following the declivities 

 and winding through the valleys, find their way on the one side 

 or the other to the sea. In this case, the general direction of the 

 rivers will be at right angles to the ridge which traverses the coun- 

 try. The rapidity of their streams will be proportionate to the 

 steepness of the declivity, and their length to the distances of 

 the prevailing ridge from one or other coast. 



126. Example in the Eastern Continent- An example 

 of the play of this principle is presented in the great eastern 

 continent, where, as has already been explained, the moun- 

 tain-chains running from west to east are much nearer to the 

 southern than to the northern coast. The rivers, therefore, which 

 flow towards the south, are generally shorter and more rapid, 

 while those which flow towards the north, passing over exten- 



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