CRANE. | Correlation. 323 
CORRELATION. 
The treating of ores in nearly all mining districts is at first 
crude and primitive, and usually continues so until the value 
of the deposit or deposits has been proven. Later, if the de- 
posits are found to be sufficiently rich, concentrating plants 
are erected, and the ores treated on a large scale and accord- 
ing to modern methods. In all lead and zinc districts es- 
specially, the hand jig is the first piece of concentrating 
apparatus on the ground, and is usually the last to leave. 
It is also used, more or less, throughout the life of the camp, 
either to treat small quantities of ore, as in making tests pre- 
paratory to installing a plant, or by prospectors and small 
mine owners. 
The only forms of reducing apparatus used in the early 
and more or less experimental operations of a camp are the 
bucking board and sledge. ‘These also are continued in use 
for the same reason that the hand jig is, regardless of the 
subsequent growth of the industry, and, when in the hands 
of skilled operators, these earlier and cruder forms of appa- 
ratus are very effective and efficient. We have, however, in 
this connection to do mainly with the method of treating ore 
as carried on in the larger mills. 
A few remarks in review on the methods of mining, trans- 
porting, sizing and hoisting may not be out of place at this 
point. 
Mining. 
The method of mining, 7. e., extracting the ore, is what 
may be called ‘‘underhand stoping,’’ and consists of running 
a drift and lifting or stoping up the floor; the arrangement 
of the mine being such that gravity assists in transferring 
the ore from the face to a point as near the foot of the shaft 
as is possible and convenient. 
When soft ground is worked, drifts are run as in hard 
ground ; then side drifts are run by the side of and parallel 
with the original drift or drifts, thus extending laterally un- 
til the deposit has been worked out on the level of the drifts. 
The supports for the worked-out portion are then removed 
