growth of a body of speculators and investors in mining stocks
and securities who desire professional guidance which cannot be based
upon first-hand data is creating further demand on the engineer.
Opinions in these cases must be formed on casual visits or second-hand
information, and a knowledge of men and things generally. Despite
the feeling of some engineers that the latter employment is not
properly based professionally, it is an expanding phase of engineers'
work, and must be taken seriously. Although it lacks satisfactory
foundation for accurate judgment, yet the engineer can, and should,
give his experience to it when the call comes, out of interest
to the industry as a whole. Not only can he in a measure protect
the lamb, by insistence on no investment without the provision of
properly organized data and sound administration for his client, but
he can do much to direct the industry from gambling into industrial
lines.

An examination of the factors which arise on the valuation of mines
involves a wide range of subjects. For purposes of this discussion
they may be divided into the following heads:--

1. _Determination of Average Metal Contents of the Ore._
2. _Determination of Quantities of Ore._
3. _Prospective Value._
4. _Recoverable Percentage of Gross Value._
5. _Price of Metals._
6. _Cost of Production._
7. _Redemption or Amortization of Capital and Interest._
8. _Valuation of Mines without Ore in Sight._
9. _General Conduct of Examination and Reports._

DETERMINATION OF AVERAGE METAL CONTENTS OF THE ORE.

Three means of determination of the average metal content of standing
ore are in use--Previous Yield, Test-treatment Runs, and Sampling.

PREVIOUS YIELD.--There are certain types of ore where the previous
yield from known space becomes the essential basis of determination
of quantity and metal contents of ore standing and of the future
probabilities. Where metals occur like plums in a pudding, sampling
becomes difficult and unreliable, and where experience has proved
a sort of regularity of recurrence of these plums, dependence must
necessarily be placed on past records, for if their reliability is
to be questioned, resort must be had to extensive test-treatment
runs. The Lake Superior copper mines and the Missouri lead and zinc
mines are of this type of deposit. On the other sorts of deposits
the previous yield is often put forward as of important bearing
on the value of the ore standing, but su