18 SOILS 



pronounced. The stones on the bottom of the brook 

 at home are rounder and smaller now than when 

 we first watched the tadpoles there. The spring 

 that slaked our thirst twenty years ago has worn a 

 deeper channel in the rock over which it flows. 

 Each year the apex of the Horseshoe Falls of Niag- 

 ara is four feet nearer Lake Erie. The Colo- 

 rado River, which has already worn a channel half 

 a mile deep in the solid rock of the Grand Canon, 

 is cutting deeper every year. All water, even the 

 purest spring water, has some minerals and gases 

 dissolved in it, and these help it to dissolve the rock. 

 Rain water contains small quantities of carbonic 

 acid gas and other gases, which increase its power 

 to dissolve rocks. 



SOILS BUILT WHOLLY OR PARTLY BY THE WIND 



Soils built wholly or in part by wind are not un- 

 common. In arid regions, along the sea coast and 

 near the shores of the Great Lakes, the drifting 

 sands often cover and ruin valuable soils. Some 

 of the most productive farm soils in this country 

 were made, and are still being made, by wind. A 

 noted example is the Palouse region of eastern 

 Washington, eastern Oregon and northern Idaho. 

 Here the land is a succession of rounded knolls and 

 hills, which are sometimes several hundred feet 

 high and are a rich, black, basaltic ash to the bot- 

 tom. The native Indians account for the hills in 

 a legend. They say that at one time all this region 

 was a level prairie of marvellous fertility. Wonder- 

 ful crops of maize were raised upon it by the red 

 men. One evil day they heard that the white men 

 were coming. Knowing by repute the white man's 

 greed, the Indians went to work to gather the 



