220 A TREATISE ON DREDGES AND DREDGING 



The stones, gravel and in general the residual materials left 

 after being washed out in the screens are expelled from the dredge 

 and deposited in places where they will not interfere any more 

 with the dredging operations. For this purpose different appliances 

 are used. Thus for instance in the type of dredge with revolving 

 screen iUustrated in Fig. 74 the materials coming out from the 

 lower end of the revolving screen enter into a chute, which is high 

 enough and sufficiently inclined to discharge them clear of the 

 sides of the boat. This method is convenient when dredging is 

 made by scraping the soil on parallel lines and depositing the 

 washed materials always on the same side of the dredge and above 



FIG. 75. Plan and Elevation of a Long Sluice-box. 



the ground already treated. But the most common method of 

 disposing of the washed materials is by means of the elevator or 

 tailing stacker as indicated in the Fig. 75. This consists of an 

 inclined steel trussed beam with its lower end hinged to the stern 

 of the pontoon while its upper end is supported by a gantry. Ropes 

 and pulleys allow the adjusting of this beam to such heights as 

 are required for the stacking of the materials. The upper side of 

 the beam is provided with roller supporting the endless rubber 

 belt, thus forming a proper belt conveyor of the usual type, the 

 belt being moved along by the driving drum located at the lo\\ i 

 end of the beam and geared to a special engine. The materials from 

 the screens are conveyed through a chute made of steel plates, over 



