162 GRAVEL AND PLACER MINING IN ALASKA. [bull. 263. 
The motors are of the following rated capacity: 
Horsepower. 
For digging 100 
For 10-inch centrifugal pump 50 
For 6-inch centrifugal pump 20 
For screen 20 
For raising ladder and operating lines 30 
The gravel is raised 27 feet above the water. The trommel is 5 by 
12 feet on 8 per cent grade, punched with holes that are 1^ inches in 
diameter in the upper plate, 4^ b}^ 7 inches in the middle plate 
(enlarged from smaller size), and 1-inch holes in the lower plate. 
Thirty-five per cent of the material is oversize and is dumped directly 
from the end of the trommel into 2 side chutes overboard. The trom- 
mel has 6-inch spray pipe, supplied by the 6-inch pump with water 
under 40 pounds pressure. It is estimated that the trommel plates 
will last one season. 
From the trommel the undersize falls directly to a sluice connected 
by means of a pivoted box to the main sluice in the auxiliary float. 
This sluice is 4 feet wide, 120 feet long, and 2 feet deep, is of steel, has 
a grade of 8 per cent, and is provided with Oroville Hungarian riffles 
and grizzlies to allow the material to pass to undercurrent tables, which 
have an area of 1,000 square feet (see p. 195). The dump of the main 
sluice is 8 feet above the water. Two hundred pounds of quicksilver 
are kept in the sluice and tables. 
The cost of dredging at this plant is estimated at 8 cents per cubic 
yard for the capacity above given, only actual labor, supplies, and 
superintendence on the ground considered. 
A dredge of the New Zealand type was operating on Bonanza Creek 
in the Klondike district. It is shown in PI. XXIX, B. The boat 
had been in service for several years, having been first installed 
on Lewes River. It had then been towed and hauled by cables down 
Yukon River to the mouth of the Klondike and then taken apart 
and reerected on Bonanza Creek, where its operations have continued 
during the open months since July 1, 1903. A crew of 24 men oper- 
ate the dredge and thaw the gravel in front of it. The thawing is 
done by means of 11-foot pieces of gas pipe, 12 in number, driven 
vertically into the ground. The bed rock here is a sericite-schist and 
the dredge is said to clean it well. The capacity of the dredge work- 
ing under present conditions is 500 cubic yards in twenty-four hours, 
The bucket line is equipped with thirty 3i-foot buckets, open con 
nected. The ladder is 50 feet in length and will dig 28 feet below 
the surface of the water. At present the dredge is digging to a deptr 
of 14 feet and 8 feet in front of the bow. The stacking ladder carry 
ing a steel-bucket conveyor is 38 feet long, and carries all materia 
over \\ inches in diameter, the size of the largest holes in the trommel, 
The lips of the digging buckets are of manganese steel and last foul 
