of acquisition, a resource may be thought of as scarce

if the amount ultimately available relative to demands

is small.



 Demands for resources encompass a wide variety

of materials including water, land, air, and the fertility

of the soil, woods and fibres and fuels, and many others.

The effects of production on each of these and their

effects on production would yield a separate story for

each; but no resource has been more important to the

current machine age than metals.

 Increased dependence upon machines and other

heavy structures has resulted in an increased dependence

upon metals used in their construction. Because of this

increased dependence an examination of the relationship

between expansions in production and wealth and the

supply of raw metals taken over time is important and

may reveal the extent to which the prodigious rate of

economic growth of the United States during the past

century represented the extraction of initially abundant

but limited resources.

 But not all metals are equally important, and

since we are concerned with a general relationship

between metal resources and production, our purposes

will be served by considering only the most important

metals. In terms of quantity and use some metals are

of only marginal importance, and their inclusion would