1'Ukin<;ton. 
DREDGING. 
183 
Stackers and tail sluices are of greater length than formerly. In 
early installations, without a single exception, stackers and tail sluices 
were too short, and difficulties due to improper disposition of tailings 
were of constant occurrence. Considerable areas of rich dredging 
ground, particularly when deep, have not been thoroughly worked, 
and much virgin ground has been covered by tailings to such a degree 
as to make it unworkable. The short stacker does not allow the coarse 
tailings to be discharged at a sufficient distance from the stern and at 
the proper height. There is consequently lack of room for fine tail- 
Top of tailings 
A Surface of ground 
Fig. 35.— Tailings well stacked. 
ings. In consequence the sand pump was brought into use, and the 
fines were discharged in such a way that much adjacent ground was 
covered by them. Valuable dredging ground, even now, is being- 
wasted in this way, as also by faulty manipulation of the dredge. The 
tailings have not been stacked with enough care to keep them well away 
from the sides of the cut when there is virgin ground on one or both 
sides. 
Fig. 35 shows the cross section of tailings so piled as to waste no 
ground. It is assumed that the side slope of the cut is 45°, but this is 
Top of tailings 
Surface of ground] 
Fig. 36.— Tailings poorly stacked. 
the case only when ground is very free. "B" in the sketch is the 
boundary of the cut on bed rock. "A" is the boundary of slope to 
45°. F G is equal to 2 F H. Tailings, as a general rule, should be 
so stacked that the distance from the tailings to the side of the cut at 
the surface of the water is about twice as great as the depth to which 
the dredge is digging. 
A cross section showing the result of stacking tailings badly is 
indicated in fig. 36. This cut has been filled with tailings to point A', 
the boundary of the cut at the surface. In excavating the cut, of 
