272 University Geological Survey of Kansas. 
ers and the bearings have corrugated castings, or sleeves, 
slipped on to prevent the sand and finely ground rock from 
creeping into the bearings and cutting them. Besides these 
corrugated sleeves, strips of sheet iron are bolted to the cast- 
ings, /, which are cut to fit into the corrugations of the 
sleeves; they stand perpendicular to the axis of the sleeve, 
and prevent any dirt, working along the corrugation, from 
entering the bearing. 
The wear of the rolls comes principally on the shells and 
shafts. When coarse material is crushed in the rolls, they 
usually wear along certain lines parallel with the sides, pro- 
ducing a corrugated surface, which in time will break up into 
rings. Fine material as a rule wears the shells smooth, but 
if the feed is not even the wear will be uneven also, and oc- 
curs usually on the edges, thus rounding them off. The 
edges of the rolls will also chip, and so become round, due to 
the pounding of the roll shells. Wear and breakage are 
caused more by the action of metal on metal than on actual 
abrasion of ore and metal. The wear of journals is not as 
great as formerly, as greater precautions are employed to pre- 
vent grit and dirt entering the bearings. They are often 
nearly worn off, however, before any wear whatever is de- 
tected, due to accumulations of dirt and grease. The jump- 
ing and wabbling of the rollers furnish the best evidence of 
badly worn shafts. 
The bearing casting (7, figure 52) is hollow, to reduce its 
weight. The brass half bearing, B, is set in one side, and 
receives the entire weight and pressure of the shaft. As the 
pressure is exerted from the inside outward, these brass bear- 
ings must be placed on the outside of the bearings in the 
castings, M and JM, which arrangement is readily seen on 
examination of figure 50. The brass bearings are held in 
position by C being bolted to D; also by a projecting flange 
of the bearing, B, which fits into a hollow or recess in D. 
Buckineé Boarps.—In connection with the prospect shafts 
and small hand jig plants is to be found a crude piece of ap- 
paratus commonly known as a bucking board, the purpose of 
which is to break up large masses of mineral and also to re- 
move included mineral from the accompanying country rock, 
