86 A PRIMER OF FORESTRY. 



beneath the surface of the ground. Surface fires are 

 usually far less troublesome, but in either case fires 

 which kill the trees are generally repeated again and 

 again until the dead timber is consumed. (See fig. 81 

 and Pis. XLIV, XLV, XLVI, XLYII.) 



BACK-FIRING-. 



The most dangerous and destructive forest fires are 

 those which run both along the ground and in the tops 



FIG. 81. The result of recurring fires. The forest floor has disappeared and 

 the pure white sand, which, looks like snow iu the picture, is left without 

 protection. Southern Xew Jersey. 



of the trees. When a fire becomes intensely hot on the 

 ground it may run up the bark, especially if the trees 

 are conifers, and burn in the crowns. Such fires are the 

 fiercest and most destructive of all. Traveling some- 

 times faster than a man can run, they consume enor- 

 mous quantities of valuable timber, burn fences, build- 

 ings, and domestic animals, and endanger or even 

 destroy human lives. They can be checked only by 



