THE INANIMATE ENEMIES OF THE FOREST. 65 



the slopes of mountains, is often so complete that 

 before a new vegetation can appear, the rapid 

 drainage of the slopes is attended by such a loss 

 of the soil as to render such slopes unfit to repro- 

 duce the forest trees for a period of time much 

 longer than the life of the average man. 



Forest fires are generally kindled during the 

 drier seasons of the year. Under these conditions 

 the rain which subsequently falls is apt to carry 

 off so much of the soil that, even should the trees 

 again appear, the remaining soil would probably be 

 insufficient in quantity to bring them to maturity. 



The causes of forest fires are to be found in 

 camp-fires of the lumberman, the burning of 

 brush, the locomotive spark, the lightning bolt, 

 and, perhaps, at times, to the heating power of 

 the sun's rays, concentrated by nodules of gum or 

 resin, acting as burning-glasses. 



In the case of newly-settled countries, fires have 

 been sometimes purposely started, for the purpose 

 of readily obtaining an extended pasturage. 



The rapidity with which a forest fire spreads 

 depends, of course, on the character of the trees 

 and the force of the wind. It is also, however, 

 dependent largely on the character of the soil. A 

 rocky or sandy soil permits a fire to spread much 



e 6* 



