SHERMAN] NATURE— THE SUPREME PROVIDER 195 



of North America has been ground down and transformed into 

 productive soil by the earth's gigantic ice-mill. 



But glaciers take up too much room for many to be working at 

 the same time, and since soil-production must go on, air and water 

 co-operate as parts of the earth's machiner\- that never stops. 

 When the chernical elements of air and water come in contact with 

 rock they form a powerful disintegrating force. It is a combina- 

 tion that no rock can long withstand. Whether the rock lies 

 exposed above the surface to these tools of Nature, or whether it is 

 searched out by air and water underground, the result is the same. 

 The rock crumbles away and tiims to food for plants. 



In some localities the wind gets hold of the rock with sand-blasts 

 and slowly wears it down. Sometimes it is broken up by water or 

 split apart by extreme heat or cold, and often some chemical action 

 in the rock itself causes it to break apart. A mountain-peak of 

 solid rock is about the most permanent material thing we can 

 imagine. Yet, the geologists tell us that, given time, nothing in 

 the world is more changeable than rock. 



The acids and gases released from decay-ing plant-roots and all 

 forms of vegetation combine with water and air and act as a 

 quick-process rock-to-soil converter. WTien this action is taking 

 place underground, new soil is being formed beneath the old. 



There is no sameness in natvire. When it comes to color, she 

 likes variety even in the soil. There is no question about the dyes, 

 either. She manufactures her own and they fade only when life 

 itself goes out. And so she has colored the soil mostly with 

 mineral life, some of it wath decayed plants and autumn leaves, 

 and, being alwaj's thrifty, she even uses the plumage of birds and 

 butterflies that have lived their lives and turned back to dust and 

 soil. 



While Nature's soil-producing machinery- runs continuoush* 

 with a steady output, the process seems slow to some of us who 

 reckon time by minutes and hours. With all the forces going at 

 full speed, it takes about ten thousand years to produce an inch- 

 depth of soil. This doesn't mean that every ten thousand years 

 there is an additional inch of soil evenly distributed over the land- 

 surface of the earth, for the distribution of soil is far from uniform. 

 At the present time, in some places it is several feet deep, in others 

 it may extend down a hundred feet, but its average depth is less 

 than twelve inches. In Japan and Switzerland the layer of soil is 

 so thin that when tilted it is in danger of being rapidly washed or 



