CRANE.| Prospecting, Mining and Milling Machinery. 261 
Fig. 47. Jacket and shaking screens. 
In all forms of screens used in this district a large amount 
of water is employed in carrying the material through the 
screens and in keeping them from clogging. 
Revolving Screens.— Perforated sheets of iron and also wire 
screens are formed into cylindrical or truncated, conical 
screens and fitted to frames or spiders, which in turn are 
fastened to a shaft, by means of which the screen is rotated. 
Side and end views of such a screen are shown in figure 48. 
The holes in the perforated screens are from three-sixteenths 
to five-eighths inch (for regular mill work the range is from 
