CRANE.| Prospecting, Mining and Milling Machinery. 2738 
which is largely flint. It consists of a plank box from one to 
one and one-half feet square and from three and one-half to 
four feet high, which is filled with broken stone. Upon this 
filling is placed a square or round piece of cast iron, several 
inches thick. Ore is placed upon this and pounded with a 
hammer or bucking sledge until it is reduced to the proper 
size or freed from the adhering rock mass. A post or portion 
of a log may be employed, when the piece of cast iron is 
fastened to the top. In all cases the casting forms the bot- 
tom of a shallow, three-sided box, the sides of which are 
built up out of light boards or better plank. This method of 
reducing the ore to jig size, and freeing it from foreign ma- 
terial, resembles the method of ‘‘cobbing,’’ common to many 
mining districts in the eastern countries, and also resembles 
somewhat the bucking board of the assayer. 
ORE CONCENTRATING MACHINERY. 
Concentration of the lead and zinc ores is effected, in the 
district, by a few typical and well known forms of apparatus, 
which (in the order of their importance) are as follows: Jigs; 
classifiers, as the spitz kasten and lutten ; power and hand bud- 
dles ; tables, the Wilfley being the only form of shaking table 
used ; and the round table, which has not as yet been given 
a fair trial. In the regular concentrating mills, the great 
bulk of the work is done almost entirely by power jigs; 
connected with which, and as adjuncts to them, are the slime 
and sand classifiers. The remaining forms, mentioned above, 
are seldom employed in the regular concentrating mills, but 
are used largely in the so-called ‘‘sludge’’ mills, which treat 
the waste products from the other mills. 
Jiags.—There are two forms of jigs used in this district, 
namely, the hand and steam or power jigs. 
The Hand Jig.—The hand jig is the form used when a new 
mining district is opened, and is a prospector’s apparatus for 
cleaning up small quantities of ore obtained in his prospect- 
ing operations; it is also used before definite information 
regarding the extent and value of a deposit has been obtained. 
See figures 53, 54, and plate XLII, figure 1. 
It cannot, however, be restricted to these operations alone, 
