66 OUTLINES OF FORESTRY. 



more rapidly than a damp soil. Some forests of 

 soft and readily ignitible wood have a covering of 

 moss on the soil, which permits the fire, when once 

 started, to spread with awful rapidity. 



Extensive tracts in South America, capable of 

 sustaining dense forests, and originally covered by 

 such, are now prevented from so doing by fires 

 that are systematically started every year, for the 

 purpose of obtaining a new growth of grass for 

 pasturage. 



The power of the wind in causing the destruc- 

 tion of the forest is, to a great extent, limited to 

 the edges of the forest. In the midst of the forest, 

 the trees stand so close together that they shield 

 one another from the force of the wind. If, how- 

 ever, an opening is made by the axe of the lumber- 

 man, by fire, or by any other cause, the wind may 

 cut a wide swath through the forest, and thus 

 destroy many noble trees. 



"When rivers overflow their banks, thousands of 

 acres of forest trees are often swept away, and in 

 this manner considerable changes may occur in 

 the general character of such districts. 



The timber thus thrown into the river channel 

 often forms accumulations called rafts, which, be- 

 coming fixed in certain parts of the stream, tend 



