40 ECONOMIC GEOLOGY OF SILVERTON QUADRANGLE, [bull.182. 
for working purposes. But the more approved practice is to fill in 
the slopes as the work proceeds, blasting out material from the walls 
if necessary. In many cases this filling is successfully combined with 
systematic prospecting of the wall rock on both sides of the vein, often 
resulting in the discovery of ore which would otherwise have been 
overlooked. Underhand stoping is, however, practiced in a few mines, 
as in the Sunnyside, where the proportion of waste which it is neces- 
sary to move is small in comparison with the ore. 
Machine drills are not generally employed, save in running long 
crosscuts. The progressive Silver Lake mine began, however, to 
emplo}^ several Siemens and Halske electric drills in its stopes in 1899. 
In mines of moderate output the ore is taken directly from the ore 
chutes and run out in single cars pushed by a man or a boy. In the 
Silver Lake mine the ore collected from the various drifts and levels 
is all dumped into ore bins in the main underground station on the 
adit level, and thence taken out to the mill in a train of cars drawn 
by a mule. In the Revenue tunnel, which is over 7,400 feet in length, 
and from which the daily output is some 200 tons of crude shipping 
ore and an additional amount of milling ore sufficient to furnish 30 to 
40 tons of concentrates, the ore is drawn out in a train of cars operated 
by an electric locomotive. The tunnel is furnished with a double 
track, but practice has shown that even in an adit of this length a 
single track is amply able to accommodate a much greater output 
than that now handled. 
Many of the mines being situated above timber line in the high 
basins, frequently from 2,000 to 4,000 feel above the main roads, the 
proper location of the mill and the mode of transportation of the ore 
and concentrates to the nearest railway are problems which must be 
solved for each mine. Owing to the scanty and intermittent character 
of the water supply, it is seldom practicable to mill the ores at the 
altitude of the adit tunnel. An exception must be made in the case 
of the Silver Lake mine, where water for the mill is obtained by pump- 
ing from the adjacent lake. But in most cases the mill is built any. 
where from a few hundred to several thousand feet below the mine. 
The primitive method of packing the ore down on backs of burros to 
the shipping point or to the mill is in use by nearly all the small mines 
and prospects. But in well-equipped mines, located above timber 
line, the wire-rope tramwa} 7 performs an office which makes it indis- 
pensable in the mining development of so rugged a country. These 
tramways are of various patterns, from the lightly constructed Huson 
tram, with its small fixed buckets and single rope, to the substantial 
Bleichert, with large detachable buckets drawn over a fixed rope and 
supported by well-constructed towers of timber. The Bleichert tram- 
way of the Camp Bird mine in 1899 was running about 45 buckets, 
each bucket carrying about 700 pounds of ore. One man is able to 
dispatch 350 buckets a day. This, however, is by no means the full 
