166 USES OF FORESTS AXD OTHER 



stance from the air. All the material which goes 

 into the air when we burn wood came from the 

 atmosphere during the growth of the plant. When 

 the tree dies, or when its leaves and branches fall 

 in the perennial death of its parts which attends 

 the growth of the whole plant, this carbon drawn 

 from the atmosphere is more or less built into the 

 soil, giving it the blackish look which is always 

 found in fields recently won from woodlands. 

 This mixture of decayed vegetable matter serves 

 in several important ways to make the soil fruitful. 

 The farmer has to imitate the natural process which 

 goes on in the forest by ploughing in clover, buck- 

 wheat, or other crops in order to introduce the 

 vegetable matter into the soil and so maintain its 

 fertility. 



The utility of forests to man, though best exhib- 

 ited in the processes by which they make, save, 

 and enrich the soil, is shown in many ways. From 

 the forests we derive the construction timber, which 

 constitutes a large part of all houses, and of itself 

 is sufficient for the greater part of the dwellings 

 inhabited by man ; without this supply hardly one 

 of our arts could be maintained. Even in our 

 large cities, where the outer walls are of masonry, 

 the greater part of the structure is composed of 



