Report on the geology of South Carolina; . ; and it doesnot follow that the previous working was imperfect, because gold is found. The iron pyriteswhich the beds contain, by exposure becomes oxydized, and gold is liberated. OF SOUTH CAROLINA. 281 The gangue in the veins requires crushing, and often a high degree of levigation, in order to hb-erate the gold. To accomphsh this there are two or tliree machines in common use. Fig. 43 is theChilian mill, which consists of a stone wheel, about five feet in diameter, and shaped like a mill-stone. This is fixed upon an axis, upon which it turns, very
Report on the geology of South Carolina; . ; and it doesnot follow that the previous working was imperfect, because gold is found. The iron pyriteswhich the beds contain, by exposure becomes oxydized, and gold is liberated. OF SOUTH CAROLINA. 281 The gangue in the veins requires crushing, and often a high degree of levigation, in order to hb-erate the gold. To accomphsh this there are two or tliree machines in common use. Fig. 43 is theChilian mill, which consists of a stone wheel, about five feet in diameter, and shaped like a mill-stone. This is fixed upon an axis, upon which it turns, very close to a vertical shaft, which alsorevolves. The door is composed of hard stone, enclosed by staves, so as to retain the water andore placed under the wheel. It is obvious that when this passes over the ore, an enormous crush-ing and grinding force is exerted; and, for very refractory ores, it is an excellent contrivance. Mer-cury is placed with the ore, in the mill, or the amalgamation takes place as the ground ore andwater passes 65 282 GEOLOGICAL SURVEY In this State what is supposed to be an improvement on this, is used. Fig. 44 is a sketch of this machine, which consists of four cast-iron wheels, each weighingabout 1500 pounds. They revolve in a circular trough, composed of four segments, weighing 3600pounds. The wheels make from six to eight revolutions round the circle per minute, and grind, ofordinary ore, from fifty to seventy bushels a day. Six to eight pounds of mercury are used at atime, in the mill; a small stream of water flows into the trougii, which carries olf the fine matter,as the ore is ground. The ore is fed in by a man with a shovel. Some care is requisite to regulatethe quantity admitted, and the velocity of the wheels. The water, as it escapes, passes over mer-cury, placed in the riffle-box, a, so as to catch any gold not taken up in the mill. Notwithstandingthis, I have rarely examined the water, as it escapes from the rifile, without finding bo
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