SEDIM ES TA TION. 87 



the fragments to pieces one against another. On 

 reachin^j^ the plains, these broken and partially- 

 rounded pieces are washed into the comparatively 

 quiet current of a river, and in course of time, by 

 the constant motion of tlie water and the attrition 

 caused by it, assume the character of pebbles. The 

 river slowly carries the pebbles towards the sea, and 

 all the time their size is diminishing. Instead of 

 pebbles they become gravel ; the particles of gravel, 

 still diminishing in size, become sand ; and the sand 

 — more especially if the river be of any considerable 

 width — tends to choke its bed. The remedial action 

 of the river is to carry the sand, and the broken 

 earth washed from its banks, down to the sea, where 

 it deposits them, at a distance more or less great 

 from its embouchure, according to the weight or 

 tenuity of the particles and the strength of the cur- 

 rent. Finally, the smaller stones are thrown upon 

 the shore, the sands are deposited farther off in 

 the sea, and the light mud is carried away and 

 slowly deposited at a still greater distance. The 

 muddy water of the Amazon is distinguishable at 

 sea nearly a hundred miles from the embouchure 

 of the river. 



The rocks of the seashore also yield their tribute 

 to the bottom of the sea, and assist very materially 

 to fill up the deej^er abysses, the slow and continual 



