176 ARE SOILS ENRICHED, IMPOVERISHED, pt. rn. 



the floods poured into it in the rainy seasons from 

 inclined channels. The consequence is ponding back, 

 the river rising on itself, overflow, and deposit from the 

 overflow : but the banks, catching the first and heaviest 

 deposit, grow moi^e quickly than the plain, and the last 

 yard protruded at the level of the sea, by preventing 

 the spreading of the water, tends to force it over the 

 yard behind it, and to raise that yard above the level 

 of the sea ; and so every yard raises the yard 

 behind it, in succession, to the highest point of the 

 alluvial plain ; though in any part, and particularly in 

 the higher part, the growth of the plain may (from ex- 

 cess of the longitudinal over the lateral deposit) keep 

 pace with the growth of the banks. 



Thus it is that a river is enabled to build itself a 

 channel 100 or 200 miles out to sea, the sides of wdiich 

 shall not only confine for three parts of the year the 

 waters which built them, but these banks shall rise high 

 above the level of the sea. This at first appears im- 

 possible. Yet every day, in every quarter of the globe, 

 this impossibility is being performed. 



And ])ossibly banks thus built may tend to assume 

 that slope or gradient lengthwise which, when flooded, 

 would allow the water to escape sideways at the same 

 instant, and at the same depth, everywhere. And this 

 tendency to a gentle simultaneous overflow of the whole 

 banks prevents their erosion and the enlargement of the 

 channel in the flood season, and, I think, is the reason 

 of the small size of the channels of rivers in alluvial 



