146 
GRAVEL AND PLACER MINING IN ALASKA. 
[BULL. 263. 
Dropoffs are not used in any of the sluices seen in Alaska or the 
North. Grade is lacking-, it is true, yet in the case above mentioned 
there was a space of 25 feet vertically between the end of the sluice 
and the creek bed which served as the floor of the dump. One or two 
drops of 6 inches in the short sluice would seem entirely practicable, 
and would certainly be advisable. Cemented gravel does not occur 
generally at Atlin, but layers of clay are found in the pay streak. 
Such clay can not be properly disintegrated in a short sluice, but will 
roll in balls through the entire string of boxes, carrying with it not 
only the gold inclosed in its mass, but picking up gold already lying 
at rest. 
A useful device to tighten the bottom boards of sluice boxes 
before nailing is shown in fig. 31. It is claimed that no tongue and 
groove are necessary with this appliance. 
In the Atlin district the mining operations are hindered by heavy 
floods in the early part of June. At the property of the Societe 
Miniere on Bowlder Creek, it is the practice to cover the sluice with 
Fig. 31.— Side-board tightener used in making sluice boxes, Atlin, British Columbia. 
a series of small protective dams, so that the debris brought down 
by the annual flood may not injure the boxes. This debris is after- 
wards piped off, at the cessation of the high water, and the dams 
are then removed. 
The following details of this plant were kindly furnished by 
M. Henri Maluin, of the Societe Miniere de la Colombie Britannique, 
and will be of interest: 
The property on Bowlder Creek operated by the Societe" Miniere de la Colombie 
Britannique is situated in the Atlin mining division of the Cassiar district, British 
Columbia,' 12 miles from the town of Atlin, on Atlin Lake. Operations were started 
in June, 1901, and the property has been worked continuously during the open 
season up to the present time. The product of gold has been 3,440 ounces, worth 
$16.63 per ounce. The gold is rather coarse, and nuggets up to 10 ounces in weight 
are found. Work is carried on both in the present bed of Bowlder Creek ami on 
benches lying at approximately the same level as the creek bed. The gold-bearing 
channel is about 150 feet wide, the grade of the creek bed varying from 6 per cent 
to as high as 10 in the upper end. Where work is now carried on it is 6.1 per cent.. 
The depth of ground averages from 25 to 50 feet, of which the lower 6 feet is consid- 
