270 University Geological Survey of Kansas. 
A roller is made up of three parts besides the shaft, namely : 
The core, wedges, and shell. In 7, figure 51, is shown the 
front roller, side view; in 3, the back roller, also side view ; 
and in 2, an end view of the front roller, showing shaft, core, 
wedges, and shell. 
Fig. 52. Details of roll bearings and star wheel. 
At 41s shown a section of the shell of the front roller, at 5 
the end view of the core, and at 6 a section of the core. ‘The 
surface of the core is usually grooved, so as to present a rough 
surface to the wedging. ‘The core is hollow, chiefly to make 
it lighter to handle; also to lessen the expense. At 7 are 
shown the wedges and their arrangement as employed in 
fastening the shell to the core. They are driven in place 
dry, and, on becoming wet, swell, when it is impossible to re- 
move them without breaking up the shells. 
Those portions of the roller shafts lying between the roll- 
