376 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1914. 
We now come to the more important methods of gold recovery by 
which the outout of the field is being maintained after the drift 
miners have extracted all that is possible by their simple and inex- 
pensive appliances. There are, as we have seen, two kinds of gravel, 
one in the valleys and the other on the high terraces, and to extract 
the remainder of the gold two separate methods must be thus 
employed. 
The valley gravels are worked down to a certain depth by very 
strong and specially constructed dredgers, with internal revolving 
trommels or sereens, and extensive sluice boxes with the usual riffles 
to catch nuggets and gold grains. The terrace gravels are removed 
by hydraulic giants, and washed through flumes and sluice boxes 
into the already depleted valley bottoms, and when all these compli- 
cated operations are completed the physical character of the gullies 
is completely changed. 
The dredging operations are mainly conducted by two companies. 
One of these is the Boyle Concessions (Ltd.), and the other the 
Yukon Gold Co., the principal partners in which are the Messrs. 
Guggenheim. The Boyle Concessions (Ltd.) has taken over the 
holdings of the Canadian Klondike Mining Co., and controls and 
operates the properties of the Bonanza Basin Gold Dredging Co. 
and the plant of the Granville Power Co. The company has holdings 
on the Klondike Valley and other creeks, covering altogether about 
40 square miles, and at present its operations are confined mainly 
to dredging the valley gravels. The Yukon Gold Co. has. both 
dredgers in the valleys and hydraulic monitors at work in the upper 
white gravels. 
The dredging process is an interesting and remarkable one, and pro- 
duces curious effects. To wander up a lone glen with a mere trickle 
of water in it, and suddenly to come round a corner and confront a 
solitary large dredger, grinding away among peat bogs, wooden huts, 
and old dump heaps, is a surprising apparition to one who always 
associates dredgers with docks and navigable estuaries. But this is 
what can be seen in several creeks and dry gulches amid the Klondike 
hills. The plant is transported piecemeal, with great labor, to the 
patch of alluvium where it is required; a large square hole is then dug 
in the ground large enough to float the structure, and there it is put 
together, built up, and set agoing. The buckets scoop out the gravel 
at one end, and the stones and sand are dropped out in a bank behind 
at the end of a long conveyor, while the fine mud runs out by a sepa- 
rate orifice. This pond or tank is thus part of the working plant, and 
the dredger slowly carries along with it the water on which it floats, 
as the original stream is far too small to support the massive hulk. All 
the water in the stream is, of course, required to help in keeping the 
basin full, and to prevent its fluid from becoming too thick in conse- 
