304 LOGGING 
the scraper to the working point. The efficiency of this method 
is less than that of a shovel since there is a good deal of lost tune 
incurred especially on long hauls or on stony ground. The 
average output per hour of scraping time on one operation was 
16.7 cubic yards of earth.^ 
ROCK EXCAVATION 
Previous to excavation, rock is broken by an explosive into 
fragments that can be handled readily. 
It is transported chiefly in carts, wagons and cars, although 
it may be moved for short distances on wheelbarrows or thrown 
out by hand in shallow cuts. 
A cubic yard, place measure, of rock increases from 60 to 
80 per cent when broken up. On an average only 60 per cent 
as much yardage of rock can be hauled as of earth. 
Payment for the removal of rock which is classified as "loose 
rock" and "solid rock" is on the basis of the cubic yard, "in 
place." 
A. BLASTING 
The holes in which charges are placed are usually bored with 
hand drills. The diameter and spacing of holes depend upon the 
kind of explosive used, the character of the rock and the method 
of handling it. As a rule, the holes are spaced a distance apart 
equal to their depth, although in hard rock they often are placed 
closer together. Close spacing increases the amount of drill 
work required and the quantity of explosive used, although it 
is often more economical because of the smaller size of material, 
which makes handling cheaper. 
Drilling.- — Hand drilling usually is preferred for logging work 
because of the limited amount of rock moved and the difficulties 
of transporting drilling machinery and equipment to the site of 
the work. Power driven drills are used on some operations on 
which there is a large amount of rock work to be done. Most of 
these drills are operated by compressed air piped from a compressor 
on the shovel or from a special air-compressing equipment, driven 
^ See Logging in the Douglas Fir Region. By W. H. Gibbons, Bui. No. 
711, U. S. Dept. of Agriculture, page 188. 
2 See Handbook of Rock Excavation, by H. B. Gillette, McGraw-Hill 
Book Co., Inc., New York, 1916, pp. 21 to 36. 
