136 PHYSIOGRAPHY. [cH. ix. 



and, at length, a complex system of branches is established, 

 all tending to a common channel which runs down towards 

 low water. Even without going to the sea-side, one may 

 often see similar effects near a way side puddle which re- 

 ceives the muddy drainage of the road. No imagination 

 is needed to compare the miniature system of branching 

 streams, produced in either of these cases under one's eyes, 

 with the drainage system of a river basin. The model 

 is in fact complete in almost every point. There is the 

 main stream, with its side feeders, running down to the 

 sea ; and, it may often be seen, that one little system of 

 streams is separated from another by an intervening space 

 which represents a water-parting. 



Suppose now that a portion of the sea-bottom were to be 

 upheaved, and appear above the surface of the water as a 

 great mud-flat. From what has just been said, it is easy to 

 judge at once how it would be drained. When rain fell 

 upon this new-born land, it would be sure to find some 

 slight rise and fall of the surface, and the gentlest fall is 

 sufficient to determine that the rain shall run in this direc- 

 tion rather than in that. The very fall of the pattering 

 rain-drops would produce little dimples on moist ground, 

 and thus give rise to superficial irregularities. As the water 

 flowed off in runnels, it would wash away fine particles of 

 the mud ; and thus every shower would find better channels 

 scooped out to receive the drainage. The streams would 

 certainly not run down to the sea in parallel straight lines, but 

 a number of neighbouring streams, all tending to the lowest 

 level, would soon be gathered together in a common channel, 

 something like that shown in Fig. ^;^. If the action went 

 on for a long time, the water- channels would get worn wider 

 and deeper, while the sides of the streams would be washed 

 by the rain into sloping banks. So close indeed is the 



