FORM OF THE SURFACE. '551 



posited at the bottom of the sea, and it must, in the 

 process of time, alter the relative levels of the ocean 

 jiud the land. Islands have been lifted by volcanic 

 power from the bottom of the sea, and many districts 

 in South America have been depressed by the same 

 causes. 



Changes as extensive have been, in all probability, 

 effected by forces " equally or more powerful, but acting 

 with less irregularity, and so distributed over time as to 

 produce none of those interregnums of chaotic anarchy 

 which we are apt to think (perhaps erroneously) great 

 disfigurements of an order so beautiful and harmonious 

 as that of nature."* These forces are, without doubt, 

 even now in action. 



Had it not been for these convulsive disturbances of the 

 surface, the earth would have presented an almost uni- 

 form plain, and it would have been ill-adapted for the 

 abode of man. The hills raised by the disturbances of 

 nature, and the valleys worn by the storms of ages, 

 minister especially to his wants, and afford him the 

 means of enjoyment which he could not possess had the 

 surface been otherwise formed. The " iced mountain 

 tops," condensing the clouds which pass over them, send 

 down healthful streams to the valleys, and supply the 



miles per hour, it is not a little curious to consider that the agi- 

 tation and resistance of its particles should be sufficient to keep 

 finely comminuted solid matter mechanically suspended, so that it 

 would not be disposed freely to part with it, except at its junction 

 with the sea-water over wbich it flows, and where, from friction, 

 it is sufficiently retarded. So that a river, if it can preserve a 

 given amount of velocity flowing over the sea, may deposit no 

 very large amount of mechanically suspended detritus in its course 

 from the embouchure, where it is ultimately stopped. Still, how- 

 over, though the deposit may not be so abundant as at first sight 

 would appear probable, the constant accumulation of matter, how- 

 ever inconsiderable at any given time, must produce an appreciable 

 r-ffect during the lapse of ages." Sir Henry De la Beche's Geo- 

 logical Researches, p. 7 '2. 



* Sir J. F. W. Herschel : Preliminary Treatise. 



