roots of the previous crop and exposed the new soil to wind and water. 

 This deep soil, brought to the surface, lacks the product of organic change 

 going on near the surface, and it also fails to hold together mechanically. 

 Such deep plowing has probably contributed to the ruin of the soil in many 

 parts of the flat farm country. 



From better ways of working the soil we learned also how to conserve the 

 soil, and eventually to keep it from becoming exhausted. Millions of farms 

 have been allowed to deteriorate so that they can hardly be reclaimed. At the 

 same time, we can see other farms continuing to yield year after year, in 

 spite of more intensive working. 



Earth and Water We depend upon rain for the growth of plants; yet 

 every year the rain washes tons of earth into streams and rivers. The quantity 

 of earth carried down to the sea every year is estimated to be worth over a 

 billion dollars. Not only is this a direct loss of agricultural resources, but it 

 also interferes with the navigation of streams and chokes the harbors. We 

 have to spend millions of dollars every year to dredge rivers and harbors to 

 remove this soil. As we saw, it is the mining of timber that has been largely 

 responsible for disturbing the water balance and for injuring the soil, by 

 destroying the absorbent forest floor (see pages 589 ff,). Conversely, reclaiming 

 desert lands depends upon supplies of water from regions that are continually 

 covered with forest. 



The Forest and Water^ Every year, as the snows on the hills begin to 

 melt, the water rushes down the hillsides in the deforested regions. The 

 streams overflow their banks, and the torrents tear down and destroy every- 

 thing in their path. The annual damage done by floods in this country is 

 estimated to be equal to one hundred million dollars. This takes no account 

 of the destruction of human life that often accompanies the floods. 



For agricultural purposes, water must be had in abundance throughout the 

 summer. The destruction of forests in one region has often resulted in the 

 ruin of agriculture and in the migration of people in a distant valley. Streams 

 that depend upon deforested areas for their water will be too full in the spring 

 and will run too low in the summer. The forest influences navigation on the 

 larger streams in two ways: (1) it maintains a steady flow of water, and (2) it 

 prevents the filling up of a stream with soil. 



Water Power As our industries expand, we are pressed to find sources 

 of energy for driving our machines. The consumption of coal has increased 

 so rapidly that the earth's supply threatens to be exhausted. Oil, which is 

 also limited in quantity, seems to be more valuable for use in cars, trucks, air- 

 planes and boats. Water power seems to be the only source of energy that is 

 constantly renewing itself. But to maintain the service of waterfalls, we must 

 be sure that the water supply will be steady. And this in turn depends upon 



iSee No. 2, p. 656. 

 645 



