306 
LOGGING 
Character of rock 
Feet 
Granite 
7 
11 
16 
Trap (basalt) 
Limestone 
Hand Drill. — The hand drilling method is similar to jump 
drilling, except that the operator sitting down holds the drill with 
one hand and strikes the drill with a 4^-pound hammer held 
in the other hand. These are used only for holes of small diam- 
eter, 3 feet or less in depth. This drill may be used for hori- 
zontal or inclined bores. 
Hand drill rods are made of octagon steel and range in size 
from f of an inch in diameter, with a f- or 1-inch bit, up to a 
|-inch rod with a Ij-inch bit. A 1-inch drill rod is the maximum 
size practicable. Chisel-shaped bits, similar to those for jumper 
and churn drills, are used. 
B. EXPLOSIVES^ 
Explosives for blasting belong to two general classes: 
1. High explosives which require an intermediate agent for 
explosion, such as a fulminate detonator. 
2. Low explosives which can be fired by direct ignition. 
High Explosives. — For blasting purposes these are marketed 
in the form of dynamite, giant powder, gelatine, and some other 
similar products. The more powerful forms are composed of a 
mixture of nitro-glycerine and some absorbent, such as sawdust 
and wood pulp, while the lower grades contain explosive salts 
in addition. Nitro-glycerine undergoes no change when com- 
bined with the absorbent, the latter acting only as a cushion and 
as a means of solidifying the liquid. 
High explosives are made of varying strengths and are graded 
on the percentage of nitro-glycerine they contain. The standard 
grades range from 75 per cent down. Those most frequently 
used are 40 and 60 per cent, the former being preferred for many 
classes of work. 
High-grade dynamite explodes with great suddenness and will 
shatter rocks and stumps into small fragments. It is especially 
* The author is indebted to publications of the E. I. DuPont d^ Nemours 
Co., for many facts regarding explosives. 
