Developing Mineral Properties. | 207 
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Fig. 19. Method of removing bottom of drift by subdrifting. 
employed, or side drifts employed without elevating the sets. 
This method is seldom employed except in very soft, wet 
ground, and in relatively small deposits. The stoping up of 
the floor of a drift in soft ground is accomplished by running 
a second drift directly under the first. Figure 19. If the set 
of timbers in the first drift are furnished with mud sills these 
sills can be used as caps to the second set of timbers below ; 
if the posts in the original drift are simply set in hollows in 
the floor, the whole space of the first drift must be cribbed or 
cogged up. Todo this, rough timber, generally poles, rang- 
ing from four to six inches in diameter, are built up in the 
form of a crib or pen, similar to the arrangement of the crib- 
bing in the shaft. Figure 19. When the cribbing reaches 
the roof it is made perfectly firm by wedging down from above. 
The wedges are long enough to allow for tightening at inter- 
vals if necessary. The capping timbers of the sets in the 
drifts below are then placed under the bottom timbers of the 
cribbing, posts are put in place, and a new drift is formed, 
which can be advanced along the course of the former or pro- 
ceed in any direction desired. 
If stoping drifts run under other drifts, the timbers of which 
have no mud sills, the posts of the upper drifts are liable to 
break through the roof of the stope drift, thus causing a 
cave-in, which is liable to crush the timbers below. Crib- 
