62 Our Field and Forest Trees 



border a railroad so that the sparks from the 

 engine can do no mischief. Or such a line may 

 surround a township or a piece of land full of 

 valuable timber. 



A fire which goes through the tree-tops — what 

 foresters call a "crown fire" — is a fearsome 

 thing. It makes its own draft, and often it 

 travels faster than a man can run. Crown fires 

 almost always start from surface fires, and occur 

 when the woods are very dry and there is a strong 

 wind blowing. Close behind the blaze in the 

 tree-tops, comes a surface fire, also moving on- 

 ward very fast. The strong, upward draft of 

 heated air carries with it an immense quantity 

 of burning cinders and bits of bark all aflame. 

 The wind blows these far in advance of the great 

 conflagration, and they drop into the 'forest and 

 start new fires. 



When leaf mold is very deep, sparks can feed 

 through it as they do in punk. Fire may burn 

 in this way for weeks beneath the surface of the 

 ground, sometimes sending up a little smoke, 

 sometimes showing no sign of its presence. Heavy 

 rain may fail to quench such a fire as this, and its 

 flames may break out long after all danger is 

 thought to be over. 



Ground fires like these can sometimes be checked 

 only by digging a trench across their path, deep 

 enough to go through dead leaves, moss, and 

 mold into the mineral soil beneath. 



