pubington.] HYDRAULIC MINING. 141 
The duty given above is based entirely on statements made by the 
operators, and owing to the short amount of running time which has 
furnished the data, no particular case can be considered of high 
authority. It will be seen, however, that the different operations in 
each separate province present a certain amount of agreement. 
In stripping operations where the ''frozen muck" is removed by 
water, ground sluicing appears to be nearly as efficient as the use of 
water through the nozzle, both iu the interior and Seward Penin- 
sula. This peculiar material, from 50 to 75 per cent ice, is easily 
thawed when exposed to the atmosphere and to flowing water. It 
appears rather to be melted than cut away, therefore the impact of a 
hydraulic stream adds little to the efficiency of a given quantity of 
water. 
It is stated by the Klondike operators that were the "White 
Channel" gravels unfrozen the duty of the inch would be twice as 
large. This is not impossible, as the bench gravel presents most 
favorable characteristics for easy handling. In its frozen state, how- 
ever, the bank has the consistency of fresh granite. 
In Seward Peninsula the instances tabulated are mostly those where 
hydraulic lifts are employed. The duty has been given in terms 
of the total amount of water used, including bank head, monitor, and 
elevator water. In the cases where elevators are used the grade and 
dimensions refer to the bed-rock sluice leading to the throat, and do 
not refer to the tail sluice. 
HANDLING OF BOWLDERS. 
The handling of large bowlders in northern hydraulic operations 
does not present serious problems. Where hydraulicking is possible 
it is generally found that all the material is small enough to go 
through the sluice. In the districts visited during the season's work 
the Atlin district, of northern British Columbia, was characterized by 
gravels containing large bowlders, which had to be derricked out or 
sledged in the pit. The practice of "bulldozing" or "plastering" 
bowlders to break them, by placing sticks of powder on top, covered 
with a mud cap, is not to be recommended on account of the expense 
of powder. Sledging into pieces small enough to be sent to the sluice 
will generally be found the cheapest method, especially as bowlders 
consisting of hard and tough rocks are not frequently encountered. 
Mr. J. D. Hauer, in a recent article, states that in general contract 
work under given conditions the cost of sledging sandstone bowlders 
varied from 1 to 9 cents per cubic yard; " mud capping" or "bulldoz- 
ing" costs from 18 cents to as much as 51 cents; "blocking," or 
breaking by drilling and blasting, costs from 11 to 18 cents; while the 
method of placing the powder charge under the bowlders costs from 
a Engineering News, quoted in Mining and Scientific Press, Feb. 9, 1905. 
