Shells are used for ornament in poor communities but cease to be so used in a higher state of advancement, and thus their saleability ceases.

Furs cease to be generally marketable in northern climes, when the fur-bearing animals are nearly killed off and the fur trade declines.

When tobacco was the great staple of export from Virginia, everybody was willing to take it, and its market price was known by all.

It served well then as the chief money, but, as it ceased to be the almost exclusive product of the province, it lost the knowableness and marketability it had before.

In agricultural and pastoral communities where every one had a share in the pasture, cattle were a fairly convenient form of money, but in the city trade of to-day their use as money is impossible.
Thus, in a sense, different commodities compete, each trying to prove its fitness to be a medium of trade; but only one, or two, or three at the most, can at one time hold such a place.
While industrial changes and conditions affect the choice of money, in turn money reacts upon the other industrial conditions.