LEVELLING ACTION OF WATER. 5 



important inflvience, in this respect, is even yet exercised 

 by water at every moment. As it falls down as rain, 

 trickling through the upper strata of the earth's crust, 

 and flowing down from heights into hollows, it chemically 

 dissolves different mineral parts of the ground, and mechani- 

 cally washes away the loose particles. In flowing down 

 from mountains water carries their ddbris into the plains, 

 or deposits it as mud in stagnant lakes. Thus " it con- 

 tinually works at lowering mountains and filling up 

 valleys. In like manner the breakers of the sea work 

 uninterruptedly at the destruction of the coasts and at 

 filling up the bottom of the sea with' the debris they 

 wash down. The action of water alone, if it were not 

 counteracted by other circumstances, would in time level the 

 whole earth. There can be no doubt that the mountain 

 masses — which are annually carried down as mud into the 

 sea, and deposited on its floor — are so great that in the 

 course of a longer or shorter period, say a few millions 

 of years, the surface of the earth would be completely 

 levelled and become enclosed by a continuous sheet of water. 

 That this does not happen is owing to the perpetual volcanic 

 action of the fiery-fluid centre of the earth. The surging of 

 the melted nucleus against the firm crust necessitates con- 

 tinual alternations of elevation and depression on the 

 different parts of the earth's surface. These elevations and 

 depressions for the most part take place very slowly ; but, 

 as they continue for thousands of years, by the combined 

 effect of small, interrupted movements, they produce results 

 no less grand than does the counteracting and levelling 

 action of water. 



Since the elevations and depressions of the different parts 



