pubington.] DREDGING. 159 
even the experimental stage. In the interior the cost of dredging 
unfrozen ground is 40 cents per cubic yard, while the dredging of 
frozen ground by thawing ahead of the dredge with steam points 
requires an expenditure of 40 cents additional. It will be recognized 
by those familiar with dredging that such a cost is prohibitive of the 
exploitation of the average dredging gravels. 
River-bed gravels seldom average over 20 cents to the cubic yard in 
gold, locally enriched area from side tributaries necessarily being, 
excluded. It has been frequently stated by engineers that the average 
tenor of the Oroville gravels is not above 15 cents to the cubic yard. 
I see no reason to believe that the gravels cf the Alaska rivers, the 
Yukon, Tanana, Koyukuk, Kuskokwim, and their larger tributaries 
should be any higher. It is likely that only in very restricted areas 
will the tenor in gold of these streams be as high as 15 cents. It 
should be distinctly understood that Solomon River, Snake River, 
and streams of similar size in Seward Peninsula are not properly 
called dredging streams. They do not by any means fulfill the condi- 
tions implied in the foregoing geological description. While it is 
undeniable that in certain isolated cases streams having the character 
of Solomon River may be profitably dredged, the enterprise must 
be considered as lying outside the legitimate province of the gold- 
dredging industry as developed in California and New Zealand. 
A recent study of the dredging fields of California has led to the 
conclusion that while dredging is possible to a greater depth than 
formerly (60 feet in Yuba River), there has been little reduction in 
the general costs of work. Eight cents per cubic yard is the lowest 
cost which may be safely counted on at Oroville, the principal field. 
No special devices have been put into practice for breaking up 
cemented gravel, and some of the dredgers at Oroville are compelled 
to use powder to shake the bank in front of the dredge. Such prac- 
tice would have no beneficial effect in handling frozen gravel. The use 
of hydraulic nozzles attached to the ladder frame at the lower tumbler 
seat has several times been suggested by engineers for assistance in 
thawing frozen gravel as the dredge operates." Experience in hydrau- 
licking frozen bench gravels in Alaska has proved that such a device 
would be of no avail, since it is mainly the action of the sun and not 
that of the water which thaws the gravel face. The possible method 
of steam thawing is to drive long pipes from the surface into the 
ground ahead of the dredge (the practice in Bonanza Creek in 14-foot 
ground). The cost of this would probably be prohibitive when the 
depth of the ground exceeds 15 feet. 
The onl} r manner in which heat can be applied directly to the part of 
the gravel face where the buckets are digging is by means of elec 
«Levat, E. D., L'Or en Siberie orientate. 
