About 13 cubic feet of quartz weigh a ton before being disturbed; when broken to medium sized lumps 20 cubic feet may be taken as representing a ton. Although experience teaches the miner to estimate very closely the value of his sample, it is better for the tyro to have a small pair of scales with grain weights. A grain of gold, if tolerably pure, is equal to four cents. Above all things avoid the too common error of panning the pick of the rock, as a false estimate is bound to follow and only too probably eventual loss. A yard of gravel before being dug makes one and a half yards afterwards. A pan of dirt is usually about 20 pounds, although it is not well to fill quite full in actual work. Many a valuable mine has been found by following up "float" ore. Float is detached fragments of the vein or gangue, and it becomes more and more abundant as the lode is approached until it finally ceases abruptly. This indicates that the vein has been reached or passed, and a trench dug throughout the alluvial soil at right angles to the assumed line of the vein will probably reveal it. The float and mineral of course drift down hill; if the side of the mountain be saddle-shaped the float will spread out like a fan as it washes down, but if concave the force of gravity will concentrate it within a narrow space in the ravine. Float found at the foot of a hill has come, as a rule, from that hill. The nearer the vein the less worn will be the edges of the float and mineral. The gangue or vein-rock in which the metal is found may be calcite or calc spar, fluor spar, heavy spar or baryta, or quartz. Gold is almost always found in this last matrix. The upper parts of most quartz lodes are usually oxidized, that is to say, the atmosphere has acted upon the iron pyrites, freeing the sulphur and staining the quartz yellow, red, or brown, by oxide of iron. This is known as "gossan" or the "iron hat." Such quartz is frequently honeycombed and rotten. Below the water level these veins run to sulphides in which decomposition has not set in, and the gold contained in the quartz is no longer "free milling," i.e. will not give up its gold to mercury without a preliminary treatment. Whenever the explorer comes across a mass of gossan he should sink a trial shaft to the vein, as it is almost certain that below the oxidized sulphides a body of mineral exists likely to encourage mining operations. Native gold is malleable, will flatten out under the hammer, and a steel knife will cut it with ease. It almost invariably contains silver, sometimes to the extent of one-fifth. A little practice will enable the prospector to recognize it, for there is but one king metal. Much gold is derived from copper and iron pyrites, and silver and lead ores are a very large source of supply.