260 ECONOMIC PRINCIPLES

be those principally developed. Thus, by exporting the
products of the industries which depend on these resources,
the exploitation of less productive resources will be
restrained. Should the first class of resources be such as
are exhausted by use, as in the case of mineral deposits,
this exhaustion is encouraged by freedom of importation of
other products, Were it made unnecessary to import such
other products, the export of the exhaustible material of
industry might be checked, to the ultimate gain of the country.
This conservation of natural resources would be a reasonable
policy. It must be remembered, however, that the conditions
 of industry change. What appears indispensable at
one stage may be less so than is imagined, in virtue of the
advance of scientific knowledge and technical skill, while, as
has been already seen in another connection, there are not
a few cases in which unsuspected sources of wealth are
discovered, so that the exhaustion of those previously known
loses some of its importance. This principle of the
conservation of exhaustible sources of wealth must not be
made the basis of an argument, in which the exports which
are checked by restricting imports are dependent on
renewable resources. In fact, while the contention is
applicable to particular cases, it does not form an argument
‘or indiscriminate reliance on protective duties,
It is also urged that a policy of protection affords
increased employment for labour and tends to raise wages,
In so far as the level of wages depends on the effectiveness
of labour, the attraction to industries in which labour is not
effective enough to make them profitable without protection
would appear to tend to the reduction of the general effectiveness
 of the labour of the community, and thus to a reduced
 average level of real wages. So far as the contention
is based on the increase of home demand for goods of
domestic production, through the exclusion of foreign goods,
it must be remembered that the raising of the general level
of cost of production, through this reduction of efficiency,
must check the foreign demand for domestic products, and
thus go far to offset any stimulation of home demand, if it
do not more than offset it. The maintenance of free trade.