HimiNirroN.] HYDRAULIC MINING. 11? 
Reckoning the cost of lumber for a box at $4 and the labor of 1 man 
at $5 for one day to each box, such a flume would cost $4,000 per 
mile, exclusive of survey, rock work, and trestles. Jt is difficult to 
see how the cost of building even small flumes can fall below $7,000 
per mile in the South Coast province of Alaska. 
INTERIOR. 
In the interior Yukon and Tanana fields ditching is practicable and 
Is recommended in preference to mimes. There are difficulties, but 
they are not insurmountable. In the interior no large ditch enter- 
prise similar to those of Seward Peninsula has been undertaken. 
The Atlin field has afforded data regarding building of ditches, but 
conditions are hardly comparable with those in the Yukon region. 
With the exception of the small amount of bench mining in the inte- 
rior only a small amount of gravel is handled daily, and ordinarily 
water under very low heads is used. 
The future of hydraulic mining in the Klondike, Birch Creek, Forty- 
mile, Eagle, and Tanana mining districts is not promising. The gentle 
slopes of the mountains, the low grade of the creek valleys, and the 
sparse amount of water are unfavorable to obtaining a sufficient amount 
of water for hydraulicking at a working head. A peculiar drawback, 
depending on the geological history of the region, is the fact that the 
level tops of the Yukon and Tanana mountains represent a partially 
eroded peneplain of very wide extent — 300 miles from east to west and 
2<h> from north to south, approximate^. This area, in which the 
placer fields of the Y'ukon-Tanana rectangle are situated, is, as it w r ere, 
a table-land, the top of which tilts slightly to the south, and into which 
the modern streams have cut, rounding off the residual parts between 
them into low dome-shaped mountains, averaging 3,000 feet in height, 
and varying from 6,000 to 2,000 feet. 
A comparison of the topography of the South Coast province with 
|:hat of the interior is illustrated by Pis. XVIII, B, and XIX, A. In 
the interior there are no sharp declivities, no waterfalls, no sudden 
descents in the surface. The grades of creek valleys are seldom o\ er 
B feet in KM) and are commonly 1 foot in 100. (See table 8, p. 104.) 
If 2 per cent is taken as an average grade and it is assumed that a ditch 
must be three times as long as the creek on which it is to furnish 
vater under head at a lower point, it is evident that only 300 feet 
iiead would be obtained by 10 miles of ditch. Such a ditch taken 
'rom one stream would afford only 200 miner's inches of water, a fair 
iverage for the region during the four months of the summer season. 
WitJiin leading distance there are no high mountains from which to 
lraw T a supply. The alpine peaks of the Alaska Range lie to the south 
>f the Tanana, and could not by any possibility be made to afford 
yater to be used for hydraulicking. (See PI. XLI, B.) 
