Soil formation 



81 



able for plants, and vegetable growth hastens min- 

 eral decomposition. As rock, stone and sand are al- 

 ternately washed and dried by rain and wind the 

 exposed surfaces are worn and the fluids carry off 

 phosphorus and potash. When these solutions come 

 in contact with roots they are rapidly absorbed; if 

 not, some form combinations with other chemicals 

 and become solid again. 



However, Dame Nature is not so resourceless as 

 to provide but one method of soil formation. She 

 works in many ways in the evolution of plant life. 

 There are but few substances that are not contin- 

 ually oxidizing while exposed to the atmosphere, 

 and all sorts of solids are gradually disintegrating 

 into dust simply from the action of sun and air. 

 Changes of temperature assist in this process, for 

 the hardest granite gradually weakens until it 

 breaks from alternate heating and cooling in Na- 

 ture's laboratory. The expansive power of water 

 in forming ice is a force which no mineral can with- 

 stand, and as crevasses wear in rocks they fill from 

 rains, and freezes rend them asunder, shaking their 

 solid foundations. The friction of moving streams 

 wears all stones smooth, gradually grinding them to 

 powder. Millions of tons of soil are always in mo- 

 tion by the ever young wind that disports from 

 place to place. Earthworms digest the entire top 

 soil every fifty years. Each crop of weeds leaves 

 billions of little threadlike rootlets where air en- 

 ters and higher plant life is supported by their de- 



