purington.] OPEN-CUT MINING. 73 
THE STEAM SHOVEL. 
Where the ground exceeds V2 feet in depth and is unfrozen, certain 
conditions justify the installation of a mechanical excavator of large 
capacity, say 1,000 cubic yards or more in twenty-four hours. It will 
seldom be found advisable to install so large and so cumbersome a 
machine as the steam shovel in the creek diggings of Alaska, for the 
ground is rarely deep enough to justify the expense of installation. 
On bench diggings, however, where the pit can be drained by gravity, 
the steam shovel has a value which has probably been underestimated. 
The fact that water under pressure is difficult or impossible to obtain 
for the hydraulicking of benches raises the question whether these 
bench gravels can not be excavated by other means. The value of the 
steam shovel lies in the fact that it performs for the earth worker that 
portion of his work which would otherwise be most expensive. 
The ground which the shovel is to move must possess certain 
favorable conditions. In the first place, it must be entirely free from 
permanent % frost when the dipper lip of the excavator attacks it. If 
the ground holds a certain amount of permanent frost and this can be 
thawed by ground-sluicing the muck off at a period far enough ahead, 
the shovel may still have a profitable field, but its operations are likely 
to be more expensive. Heavy gravel and bowlders are easily handled 
by the mechanical excavator. It is safe to say that no quality or state 
of the Alaska gravels makes them unfit to be dug by the dipper except 
the frozen condition. 
The bed rock must be of sufficient softness to allow the dipper 
lip to dig far enough into it to recover all the gold; otherwise a 
gang of men will have to follow the shovel to clean bed rock, and a 
large part of the value of the shovel will be lost. In one attempt to 
operate with a steam shovel in the interior of Alaska it was found 
that as many men had to be employed in cleaning the bed rock as in 
the entire remainder of the plant. 
A prime essential to success, as has been proved by experience, is 
that the washing plant shall be isolated, the gravel being conveyed 
from the dipper to the sluice by some form of tramming. If cars are 
used, they should be large — 2 yards capacity, or even larger. Under 
ideal conditions the dipper will dump into cars which run by gravity 
to the hopper of the washing plant, the water being brought to the 
sluice also by gravity. The full cars would in this case carry the 
empties back to the pit. It is rarely possible, however, to find an 
auriferous gravel deposit in which such eminentl}^ fit conditions exist 
Ifor work. The tramming, even when it must be up an incline to a 
jheight of 35 feet above the pit floor, adds proportionately little to the 
expense, as will be seen by figures following. It is a common fault in 
iill steam-shovel operations that the shovel is ahead of the car discharge. 
