it is true, from disintegration by wind or rain, but
much more is caused by the earth-worm in person. That friend of
humanity, so little recognized in his true light, has a habit of
drawing down leaves into his subterranean nest, and there eating them
up, so as to convert their remains into vegetable mould in the form of
worm-casts. This mould, the most precious of soils, gets dissolved
again by the rain, and carried off in solution by the streams to the
sea or the lowlands, where it helps to form the future cultivable area.
At the same time the earthworms secrete an acid, which acts upon the
bare surface of rock beneath, and helps to disintegrate it in
preparation for plant life in unfavourable places. It is probable that
we owe almost more on the whole to these unknown but conscientious and
industrious annelids than even to those 'mills of God' the glaciers, of
which the American poet justly observes that though they grind slowly,
yet they grind exceedingly small.

In the last resort, then, it is mainly on mud that the life of humanity
in all countries bases itself. Every great plain is the alluvial
deposit of a great river, ultimately derived from a great mountain
chain. The substance consists as a rule of the debris of torrents,
which is often infertile, owing to its stoniness and its purely mineral
character; but wherever it has lain long enough to be covered by
earth-worms with a deep black layer of vegetable mould, there the
resulting soil shows the surprising fruitfulness one gets (for example)
in Lombardy, where twelve crops a year are sometimes taken from the
meadows. Everywhere and always the amount and depth of the mud is the
measure of possible fertility; and even where, as in the Great American
Desert, want of water converts alluvial plains into arid stretches of
sand-waste, the wilderness can be made to blossom like the rose in a
very few years by artificial irrigation. The diversion of the Arkansas
River has spread plenty over a vast sage scrub; the finest crops in the
world are now raised over a tract of country which was once the terror
of the traveller across the wild west of America.

THE GREENWOOD TREE.

It is a common, not to say a vulgar error, to believe that trees and
plants grow out of the ground. And of course, having thus begun by
calling it bad names, I will not for a moment insult the intelligence
of my readers by supposing them to share so foolish a delusi