GEOVND FIRES. 



85 



of rotting fallen trees. (See PI. XLIII.) In the same 

 way it climbs dead standing- trees, and breaks out in 

 bursts of flame high in the air. Dead trees lielp pow- 

 erfully to spread a lire, for in liigli winds loose i)ieces of 

 their burning bark are carried to almost incredible dis- 

 tances, and droj:) into the dry forest far ahead, while in 

 calm weather they scatter 

 burning fragments all 

 about them when they 

 fall. (See lig. 80.) 



GROUND FIRES. 



When the duft* is very 

 deep or the soil peaty, a 

 fire may burn beneath the 

 surface of the ground for 

 weeks or even months, 

 sometimes showing its 

 presence by a little smoke, 

 sometimes without giving 

 any sign of life. Even a 

 heavy rain may fail to 

 quench a tire of this kind, 

 which often breaks out 

 again long after it is be- 

 lieved to be entirely extinct. Fires which thus burn into 

 the ground can sometimes be checked only by digging 

 a trench through the layer of decaying wood and other 

 vegetable matter to the mineral soil beneath. Ground 

 fires usually burn much more slowly than surface fires, 

 but they are exceptionally long lived, and very hard to 

 put out. It is of the first importance to attack such 

 fires quickly, before they have had time to burrow far 



Fig. 80.— The effect of repeated fires. 

 Xot only the old trees are dead, but 

 the seedliiiijs whicli succeeded them 

 have perished also. Western Yellow- 

 Pine in the Black Hills Forest Eeserve, 

 South Dakota. 



