Herbert Hoover was president of the United States at the onset of the great depression.  He was also a mining engineer.  He wrote a book called Principles of Mining.  Thanks to Project Gutenberg a copy of this book is now available for free dowload at this link

The book provides a fascinating insight into old ways of expression and old ideas about mining.  Here, for example, is a paragraph from the Introduction---who could write such prose today? 

The bulk of the material presented is the common heritage of the
profession, and if any one may think there is insufficient reference
to previous writers, let him endeavor to find to whom the origin
of our methods should be credited. The science has grown by small
contributions of experience since, or before, those unnamed Egyptian
engineers, whose works prove their knowledge of many fundamentals
of mine engineering six thousand eight hundred years ago. If I
have contributed one sentence to the accumulated knowledge of a
thousand generations of engineers, or have thrown one new ray of
light on the work, I shall have done my share.

Then we have this magnificent rumination on mining investment:

The 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

And with the issue of metal prices much in mind in 2008, we can only marvel at these thoughts on what controlled metal prices then.

The demand for metals varies with the unequal fluctuations of the
industrial tides. The sea of commercial activity is subject to
heavy storms, and the mine valuer is compelled to serve as weather
prophet on this ocean of trouble. High prices, which are the result
of industrial booms, bring about overproduction, and the collapse of
these begets a shrinkage of demand, wherein consequently the tide
of price turns back. In mining for metals each pound is produced
actually at a different cost. In case of an oversupply of base metals
the price will fall until it has reached a point where a portion of
the production is no longer profitable, and the equilibrium is
established through decline in output. However, in the backward
swing, due to lingering overproduction, prices usually fall lower
than the cost of producing even a much-diminished supply. There is
at this point what we may call the "basic" price, that at which
production is insufficient and the price rises again. The basic
price which is due to this undue backward swing is no more the
real price of the metal to be contemplated over so long a term
of years than is the highest price. At how much above the basic
price of depressed times the product can be safely expected to
find a market is the real question. Few mines can be bought or
valued at this basic price. An indication of what this is can be
gained from a study of fluctuations over a long term of years.