admirable substitute for it. It forms an important article in the food of
the natives, and serves also for every domestic purpose in which oil
would otherwise be used. The demand for it is therefore very great.

In payment of these articles, the maritime states supply the interior
countries with salt, a scarce and valuable commodity, as I frequently and
painfully experienced in the course of my journey. Considerable
quantities of this article, however, are also supplied to the inland
natives by the Moors; who obtain it from the salt pits in the Great
Desert, and receive in return corn, cotton cloth, and slaves.

In thus bartering one commodity for another, many inconveniences must
necessarily have arisen at first from the want of coined money, or some
other visible and determinate medium, to settle the balance, or
difference of value, between different articles, to remedy which, the
natives of the interior make use of small shells called _kowries_, as
will be shown hereafter. On the coast, the inhabitants have adopted a
practice which, I believe, is peculiar to themselves.

In their early intercourse with Europeans, the article that attracted
most notice was iron. Its utility, in forming the instruments of war and
husbandry, made it preferable to all others; and iron soon became the
measure by which the value of all other commodities was ascertained. Thus
a certain quantity of goods, of whatever denomination, appearing to be
equal to a bar of iron, constituted, in the trader's phraseology, a bar
of that particular merchandize. Twenty leaves of tobacco, for instance,
were considered as a _bar_ of tobacco; and a gallon of spirits (or rather
half spirits and half water) as a _bar_ of rum; a bar of one commodity
being reckoned equal in value to a bar of another commodity.