Teachers' Leaflet. 



481 



greater than a dose of bitter quinine and you think it is too smah to be 

 thought of as a factor in the formation of soil. Consider, if you please, 

 how small your glass of water was compared with a river tilled from 

 bank to bank with roily water. Think of the results if the river of 

 roily water should overflow and the fine soil be deposited over the adjoin- 

 ing fields. The amount dropped by one such overflow might be but the 

 fraction of an inch, but when it .has happened a hundred times the accu- 

 mulation would be worth considering. 



But what becomes of the harder stones that start out on the journey? 

 When the softer stones became so fine that they swam away, the harder 

 stones continued to thump each other and rub against each other as they 

 did in the stocking. Now when all the remaining stones are hard it 

 becomes a case of diamond cut diamond. They continue to grind each 

 other day and night, week days and Sundays, through decades and 

 centuries. A stone that wears others not only makes them smaller, but 

 becomes smaller itself. That the children may understand what force 

 moves the stones, scatter some sand in the ripples where the current is 

 the strongest and watch the moving water catch the sand and waft it 

 down stream. The larger the stones the stronger the current necessary 

 to move them, and as a consequence the smaller stones travel faster than 

 the larger ones. In the game of one stone grinding another, when the 

 smaller ones are ground down to the size of pin heads, we have what? — 

 grains of soil. After all, a grain of soil may be only a small stone — 

 but large enough to be a back load for an ant. You now have means of 

 showing in a generic way how sand is sometimes made. There are other 

 soils. One is clay soil and may come from another kind of rock. While 

 some of it is reduced to powder by a process much like that which grinds 

 the stones in the creek, most of our clay soil comes from rock by quite 

 another kind of mill. 



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