on may pick up on a
single village site or battle-ground different implements coming from a
dozen or more different quarries or centres and made by different
tribes hundreds of miles apart in residence.

This diffusion of knowledge and things of material {105} workmanship,
or of methods of life, is through a system of borrowing, trading, or
swapping--or perhaps sometimes through conquest and robbery; but as
soon as an article of any kind could be made which could be subjected
to general use of different tribes in different localities, it began to
travel from a centre and to be used over a wide area. Certain tribes
became special workers in specialized lines. Thus some were
bead-makers, others expert tanners of hides, others makers of bows and
arrows of peculiar quality, and others makers of stone implements. The
incidental swapping of goods by tribes finally led to a systematic
method of a travelling trader who brought goods from one tribe to
another, exchanging as he went. This early trade had an effect in more
rapid extension of culture, because in that case one tribe could have
the invention, discovery, and art of all tribes. In connection with
this is to be noted the slow change of custom regarding religious
belief and ceremony or tribal consciousness. The pride of family and
race development, the assumption of superiority leading to race
aversion, interfered with intelligence and the spread of ideas and
customs; but most economic processes that were not bound up with
religious ceremonies or tribal customs were easily exchanged and
readily accepted between the tribes.

Exchange of goods and transportation went hand in hand in their
development, very slowly and surely. After trade had become pretty
well established, it became necessary to have a medium of exchange.
Some well-known article whose value was very well recognized among the
people who were trading became the standard for fixing prices in
exchange. Thus, in early Anglo-Saxon times the cow was the unit of the
measure of value. Sometimes a shell, as a _cowrie_ of India or the
wampum of the American Indian, was used for this purpose. Wheat has
been at one time in America, and tobacco in another, a measure of
exchange because of the scarcity of money.

Gradually, as the discovery and use of precious metals became common
and desirable because of their brightness {106} and service in
implement and ornament, they became the medium of exchange. Thus,