EXPLOSIVES 191 



requires a small amount of labor but a large quantity of 

 high-grade explosive, and with extremely hard bowlders 

 satisfactory results are not obtained. Snake-holing takes 

 more labor but less explosive and generally gives satisfactory 

 results (Fig. 172). Block-holing requires a great amount 

 of labor, but good results can be had in all classes of rock 

 with a minimum of explosive (Fig. 173). Unless the nature 

 of the rock in the locality is well known, experimental work 



TA/WP//VG 

 DYNAM/7E P/R/MEft 



:.. ;■--! 



After E. I. du Pont de Nemours & Co. 



Fig. 173. Breaking bowlder by block-holing 



should be done to determine which of these three ways is 

 the most economical. 



Hardpan. A stratum of hardpan located near the sur- 

 face may be broken up by the explosion of light charges of 

 dynamite at uniform intervals over the area. Holes should 

 be bored into the hardpan with an auger, and a small charge 

 of dynamite tamped in and exploded with a safety fuse. 

 The depth of the charge and the quantity of explosive 



needed should be determined by experiment. A low grade, 

 20 per cent, is ordinarily used. 



Tree planting. Tree planting in hard ground may be 

 facilitated by the use of dynamite in breaking up the ground 



