used for growing corn, and later it may be devoted to
the building of houses, or, as at Slough, to a repair depot for motor
vehicles. It need hardly be said that the land will, as a general
rule, be put to the use in which its value is greatest; or to speak
more strictly, in which the biggest rent, or the biggest selling price
can be obtained. But the notion of the differential advantages which a
piece of land possesses over the marginal land becomes decidedly more
complicated when we take account of this variety of uses. Let us turn
our attention, for instance, to the sites used for shop and office
purposes, and consider what we can regard as the marginal site in this
connection. Clearly it will not be the marginal land of which we
spoke above, which it only just paid to cultivate, and which yielded
no rent at all. For this will probably be agricultural land in an
out-of-the-way district, where no one would dream of setting up an
office or a shop. Any site upon which a sane man would contemplate
setting up a shop will certainly possess value for other purposes,
such as house-building. Hence the marginal site for shopkeeping
purposes will not be like our marginal farm, a site which yields no
rent.

As regards many pieces of land, there is no doubt as to the purposes
for which they can most profitably be used. This piece will command a
much higher rent as a shop site than in any other capacity; for that
piece house-building is the obvious employment; for another,
agriculture. But in quite a number of instances there is considerable
uncertainty. It is not clear whether upon this site it will be better
to erect a house or a shop, or if the latter, what kind of a shop. It
is not clear whether it will pay to use that farm land for a building
scheme; and, within the domain of agriculture, which of course
comprises an immense variety of really different industries, it is
often a very moot point indeed whether a certain field should be left
under grass, or brought under the plow. Cases of this sort are not
phantoms of the imagination; they emerge on every side as concrete
problems with which some one or other is dealing every day, and it is
these cases which constitute the marginal land for the purposes of a
particular occupation. The marginal sites for shops are the sites for
which it is only just worth while to pay rents sufficient to entice
them away from houses. And the rent for a site in Bond Street, or
elsewhere, which i