he action of the sand
itself, of the area of destroyed vegetation. Sand-deserts are not, as
used to be supposed, sea-bottoms from which the water has retreated,
but areas of destruction of vegetation--often (though not always) both
in Central Asia and in North Africa (Egypt, etc.), started by the
deliberate destruction of forest by man, who has either by artificial
drainage starved the forest, or by the simple use of the axe and fire
cleared it away.

The great art of irrigation was studied and used with splendid success
by the ancient nations of the near East. They converted deserts into
gardens, and their work was an act of compensation and restitution to
be set off against the destructive operations of more barbarous men.
But they, too, long ago were themselves destroyed by conquering hordes
of more ignorant but more war-like men, and their irrigation works and
the whole art of irrigation perished with them. One of the absolutely
necessary works to be carried out by civilised man, when he has ceased
to build engines of war and destruction, is the irrigation of the
great waterless territories of the globe. A little home-work of the
kind has been carried on in Italy regularly year by year since the
days of Leonardo da Vinci, and our Indian Government is slowly
copying the Italian example. In Egypt we have built the great dam of
Assouan, whilst in Mesopotamia it is proposed to re-establish the
irrigation system by which it once was made rich and fertile. But, as
has lately been maintained by Mr. Rose Smith in his book, "The Growth
of Nations," the vast possibilities of irrigation have not yet been
realised by the business men of the modern world. Millions of acres in
the warmer regions of the earth now unproductive can be made to yield
food to mankind and rich pecuniary profits to the capitalists who
shall introduce modern engineering methods and a scientific system of
irrigation into those areas.

The whole problem of the increase of the more civilised races and the
necessary accompanying increase of food-production depends for its
solution on the speedy introduction of irrigation methods into what
are now the great unproductive deserts of the world.

CHAPTER XXV

THE EXTINCTION OF THE BISON AND OF WHALES

The almost complete and very sudden disappearance of the bison in
North America thirty years ago does not seem to have been due simply
to the slaughter of tens of thousands of these creatures by men who