CRANE. | Developing Mineral Properties. 195 
with the ends lapping. Figure 25. The inside dimensions 
are kept the same, regardless of the space left between 
the cribbing and the rough rock walls of the shaft. The 
cribbing is kept vertical. The timbers are notched where 
they overlap, and are trimmed, if necessary, to conform to 
any projection from the wall, and if the space between the 
walls and cribbing exceeds four or six inches it is usually 
filled in with rock, forming a pack wall. If two- or three-inch 
timbers are used, the spaces between individual timbers will 
necessarily be the size of the timbers, unless they are notched 
where they overlap. The bark is often relied upon to keep 
the poles from slipping, as notches would weaken them too 
much. Quite large spaces will therefore be left between the 
timbers, which form is called ‘‘open cribbing.’’ If the dirt 
is soft at any point in contact with the cribbing, water work- 
ing down from above will tend to loosen and gradually wash 
it through the cribbing into the shaft, forming a cavity back 
of the timbers. In the course of time a cave-in will result, 
when the rush of dirt and rock against the sides of the crib- 
bing will often be more than it can stand, especially if it is 
several years old. Again, the soft material may become 
quick (saturated with water), and a run start, which would 
damage or wreck the cribbing. The result in either case is 
serious damage to the cribbing and a partially filled shaft, 
both of which would require considerable time to remedy, to 
say nothing of the danger to life attendant upon such an ac- 
cident. 
To prevent any accident in connection with open cribbing, 
it should be laced, that is, lined with boards nailed onto 
the cribbing timbers, and placed vertically in the shaft. A 
shaft when so laced is, or may be, practically impervious 
to water, thus insuring against any caving. These lacing 
boards are, of course, placed on the inside of the shaft tim- 
bers. 
_ When the shaft is sunk in a locality where the ground is 
soft and saturated with water, the cribbing is extended to 
the bed rock, where a water-tight connection is made. The 
timbers in this case must be sawed and notched so as to come 
together, forming what is known as ‘‘closed cribbing.’’ This 
