SOIL BUILDERS 17 



the town of Hadley and bestowed it upon the town 

 of Hatfield. Smaller streams, even the tiniest 

 rills, are transporting and building soil in a similar 

 manner. Sometimes this action of water is bene- 

 ficial, but usually it is injurious. The loss of farm 

 soil by erosion is discussed in Chapter XI. 

 ^Alluvial Soils. The flat lands near streams are 

 often flooded each year and receive a top-dressing 

 of rich mud that keeps them extremely fertile. 

 The Nile is a noted example, but many of our own 

 rivers, including the Ohio and Mississippi, fertilise 

 their meadows in the same way, much to the profit 

 of man. The fertile plains of Egypt, once the 

 "granary of the world, ' are not made of native 

 soils, but of soil washed down from the mountains 

 of Abyssinia, many hundreds of miles away. All the 

 rich rice and cotton fields of southern Louisiana 

 were built by the Mississippi River, of soil brought 

 from the mountains three thousand miles away. In 

 some places this soil is three hundred feet deep. 

 These various kinds of alluvial or water-built soils 

 are among the most valuable for agricultural 

 purposes. In any hilly country one can ob- 

 serve this kind of soil building going on at a 

 rapid rate. 



Besides transporting soil from place to place, 

 water also assists in soil building by wearing away 

 the rock over which it passes. It would seem 

 hardly possible that water should be capable of 

 wearing away so rapidly the hardest of rocks, were it 

 not that we can see the action going on all around us. 

 Even a single drop, falling continuously year after 

 year, will eat a deep hole in the hardest rock. 

 When a volume of water is in motion, and especially 

 when it is carrying along with it particles of soil, 

 its grinding and filing effect is much more 



