CHAPTER TEN 



HOW THE SOIL IS MADE 



The substances which we found in the soil teach us that 

 it was formed from the rocks. If we could take the sand; 

 clay, potash, soda, lime, and iron that we found in the soil 

 and put them together as Nature knows how to do, we 

 should have rock again. 



But if we should take a piece of rock and crush it to a 

 fine sand, that would not be soil, because soil cannot be 

 made in that way. It takes Nature many, many years, 

 as the rocks slowly crumble and 'decay, to change the ma- 

 terials of which they are composed into true soil with its 

 swarms of bacteria and its plant food. 



If we should dig down through the soft earth under our 

 feet, we would at last come to solid rock. This is the rough 

 and jagged crust of the earth on which rests the carpet of 

 soil. In the mountains where the slopes are steep the rocks 

 stick up through the soil. The outer parts of this soHd 

 rock are, however, always crumbling. Little particles, as 

 soon as they become loosened, either fall by their own 

 weight or are washed away. Some of the rock fragments 

 collect upon the gentler slopes and finally turn to soil. 

 This SOU is not rich and it dries out quickly, because it is 

 shallow. The soil in the valleys, as we have already learned 

 from the muddy rivulet, is deep and rich. 



Nature is slowly spreading her mantle of soil over the 

 earth. In some parts of the earth one can travel for hun- 

 dreds of miles and see no rocks. One might think that in 

 time Nature's work would be finished. But before the 

 mountains in one place have crumbled and been washed 



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