SOILS AND THEIR CHARACTERISTICS 11 



of the buckets will tend to stir up the material to such an extent 

 that its light particles may become loose again and float all aroi 

 the point of excavation. To avoid this the chain buckets are run 

 at a very low speed. As this reduces the efficiency of the machine 

 it is overcome by using buckets of very large capacity. The hydraulic 

 dredge, although very good in this kind of soil, has the disadvan- z 

 tage of stirring up the material to such an extent that it is mixed 

 with a very large amount of water. Thus an enormous amount 

 of power is required to remove a comparatively small amount of 

 material. The large amount of water diluting the mud is considered 

 an advantage when the debris is used to fill up low lands, as the 

 water facilitates the equal distribution of the material over a larger 

 area. On the other hand this surplus water is a hindrance when the 

 material is pumped into the hold of the dredge to be carried to the 

 dumping place, as in the hopper type. 



