1. The risk of continuity in metal contents beyond sample
faces.
2. The risk of continuity in volume through the blocks
estimated.
3. The risk of successful metallurgical treatment.
4. The risk of metal prices, in all but gold.
5. The risk of properly estimating costs.
6. The risk of extension of the ore beyond exposures.
7. The risk of management.

As to the continuity of values and volumes through the estimated
area, the experience of hundreds of engineers in hundreds of mines
has shown that when the estimates are based on properly secured
data for "proved ore," here at least there is absolutely no hazard.
Metallurgical treatment, if determined by past experience on the
ore itself, carries no chance; and where determined by experiment,
the risk is eliminated if the work be sufficiently exhaustive. The
risk of metal price is simply a question of how conservative a
figure is used in estimating. It can be eliminated if a price low
enough be taken. Risk of extension in depth or beyond exposures
cannot be avoided. It can be reduced in proportion to the distance
assumed. Obviously, if no extension is counted, there is nothing
chanced. The risk of proper appreciation of costs is negligible where
experience in the district exists. Otherwise, it can be eliminated
if a sufficiently large allowance is taken. The risk of failure to
secure good management can be eliminated if proved men are chosen.

There is, therefore, a basic value to every mine. The "proved"
ore taken on known metallurgical grounds, under known conditions
of costs on minimum prices of metals, has a value as certain as
that of money in one's own vault. This is the value previously
referred to as the "_A_" value. If the price (and interest on it
pending recovery) falls within this amount, there is no question
that the mine is worth the price. What the risk is in mining is
simply what amount the price of the investment demands shall be
won from extension of the deposit beyond known exposures, or what
higher price of metal must be realized than that calculated in
the "_A_" value. The demands on this _X, Y_ portion of the mine
can be converted into tons of ore, life of production, or higher
prices, and these can be weighed with the geological weights and
the industrial outlook.

MINES COMPARED TO OTHER COMMERCIAL ENTERPRISES.--The profits from
a mining venture over and above the bed-rock value _A_, that is,
the return to be derived from more extensive