208 _ University Geological Survey of Kansas. 
bing or cogging up of the upper drift is the best method, and 
is the one usually employed by the best miners. 
The method of advancing a drift in soft ground by means 
of timbers is as follows: A drift is started in the face for 
several yards; then two or three sets of timbers consisting of 
two posts, a cap and a mud sill are put in position facing the 
direction in which the shaft is run. Over the cap of the set, 
farthest in advance and on the outside of the post, stakes or 
poling boards are driven. ‘The poling boards are generally 
split poles made from four- or five-inch green poles and are 
sharpened chisel-shape at one end. ‘These stakes are often 
called ‘‘spiles,’’ and are driven with the bevel downward. 
After driving the spiles three or four feet in advance of 
the set, the enclosed dirt, if soft enough, is shoveled out. 
This is continued until the advance has been sufficiently 
great to permit placing another set of timbers, the spiles 
gradually settling until they rest upon the cap of the new set 
placed in advance. The weight of the superincumbent mass 
will of necessity press down the ends of the advanced spiles, 
so that, if driven horizontally, the pressure from above would 
push them down several inches before a new set could be 
placed, thus making the space too narrow for a normal or 
standard set to be introduced. To obviate this the spile 
is driven forward and upward at an angle of from five to 
six degrees with the direction of the advance. The angle 
depends largely, however, upon the formation worked. This 
elevation of the spile is intended to make up for the de- 
pression caused by the weight upon it from above and on 
the sides, and is sufficient to maintain the height and breadth 
of the drift until it has been advanced far enough to in- 
troduce a new set. From the above, it is evident that each 
spile rests upon two caps, at least, and occasionally upon 
three, depending, however, upon the closeness of the sets. 
A new set of spiles is driven with each set, so maintaining 
the original size of the drift and the advance. An eleva- 
tion of the spiles a few more inches to the foot will allow a 
set of longer posts, caps and sills to be placed and the spiles 
driven as before, thus increasing the cross-sectional area of 
the drift, as mentioned above. 
