THE FRIENDLY SOIL 



and taken their toll of the grist they have ground. 

 Sometimes these mills take the whole grist and leave 

 the rocks bare; but usually they leave a residuum 

 in which life strikes its roots. We do not see all that 

 the waters take from the soil. They have invisible 

 pockets in which they carry away all the more 

 soluble parts, such as lime, soda, potash, silica, 

 magnesia, and others, and leave for the land the more 

 insoluble parts. These, too, in times of flood they 

 carry away in suspension, in the shape of sand, silt, 

 mud, gravel, and the like. When the waters really 

 digest the rocks, they hold the various minerals in 

 solution, and run limpid and dancing to the sea; 

 when they have an undigested burden, they run 

 angry and turbid. 



It is estimated that the Hudson River deposits 

 in the sea each year four hundred and forty 

 thousand tons of mineral matter in solution which 

 it has taken from the land, and the Mississippi one 

 hundred and twelve million tons. Each carries 

 away about four times as much in suspension. The 

 digestive or chemical power of water, then, is only 

 about one fourth as great as its mechanical power. 

 Between the two the land is made to pay heavy toll 

 to the sea. But in time, in geologic time, it all comes 

 back. The suspended particles are dropped and go 

 to make up the sedimentary rocks, while the solutes 

 help cement the material of these rocks together, 

 and also nourish the sea life from which limestone 



169 



