CHAPTER XII 

 SOIL 



IN studying the subject of the soil, we are again 

 considering a matter with which we are all 

 familiar, since the soil is the principal covering 

 of the surface of the land, the part which is 

 nearest to us, on which we walk, and wherein 

 all our plants and trees grow. In streets and 

 roads we do, it is true, make efforts to get rid 

 of the soil ; we pave them with blocks of stone 

 or wood ; we cover up the soil to get a hard sur- 

 face over which wheels can run easily, and on 

 which we can walk in wet weather without fear 

 of sinking in. Nevertheless, the soil constantly 

 comes back again, perhaps as mud and dirt after 

 rain, or as dust in dry seasons. 



Soil, as we have already said, is made by the 

 wearing down of other substances, as in the 

 weathering of rocks, the rubbing together of 

 stones, the decay of vegetable and animal matter. 

 Even on pavements soil is always being created ; 

 for the wheels of our carriages and carts, and the 

 iron shoes of our horses, in time wear away even 

 the hardest granite, and form a layer of soil 

 which has to be swept up and carried away. 



Since soil is made by the rubbing and dis- 



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