I never tire of contemplating the soil itself, the mantle rock, as
the geologist calls it. It clothes the rocky framework of the earth
as the flesh clothes our bones. It is the seat of the vitality of
the globe, the youngest part, the growing, changing part. Out of it
we came, and to it we return. It is literally our mother, as the sun
is our father.
The soil!--the residuum of the rocks, the ashes of the mountains. We
know what a vast stretch of time has gone to the making of it; that
it has been baked and boiled and frozen and thawed, acted upon by
sun and star and wind and rain; mixed and remixed and kneaded and
added to, as the housewife kneads and moulds her bread; that it has
lain under the seas in the stratified rocks for incalculable ages;
that chemical and mechanical and vital forces have all had a hand in
its preparation; that the vast cycles of animal and vegetable life
of the foreworld have contributed to its fertility; that the life of
the sea, and the monsters of the earth, and the dragons of the air,
have left their ashes here, so that when I stir it with my hoe, or
turn it with my spade, I know I am stirring or turning the meal of a
veritable grist of the gods.
From its primal source in the Archaean rock, up through all the vast
series of sedimentary rocks to our own time, what vicissitudes and
transformations it has passed through; how many times it has died,
so to speak, and been reborn from the rocks; how many times the
winds and the rains have transported it, and infused invisible,
life-giving gases into it; how many of the elements have throbbed
with life, climbed and bloomed in trees, walked or flown or swam in
animals, or slumbered for thousands upon thousands of years beneath
the great ice-sheet of Pleistocene time! A handful of the soil by
your door is probably the most composite thing you can find in a
day's journey. It may be an epitome of a whole geological formation,
or of two or more of them. If it happens to be made up of decomposed
limestone, sandstone, slate, and basalt rock, think what a history
would be condensed in it!
Our lawns are made up of ashes from the funeral pyre of mountains,
of dust from the tombs of geologic ages. What masses of rock does
this sandbank represent! what an enormous grist in the great glacier
mill do these layers of clay stand for! Two feet of soil probably
represent a hundred feet or more of rock. Strictly speaking, the
soil is the insoluble parts of the ground-up and decomposed rocks,
after the rains and the winds have done their work and taken their
toll of the grist they have ground. Sometimes these mills take the
whole grist and leave the rocks bare; but usually they leave a
residuum in which life strikes its roots. We do not see all that the
waters take from the soil. They have invisible pockets in which they
carry away all the more soluble parts, such as lime, soda, potash,
silica, magnesia, and others, and leave for the land the more
insoluble parts. These, too, in times of flood they carry away in
suspension, in the shape of sand, silt, mud, gravel, and the like.
When the waters really digest the rocks, they hold the various
minerals in solution, and run limpid and dancing to the sea; when
they have an undigested burden, they run angry and turbid.
It is estimated that the Hudson River deposits in the sea each year
four hundred and forty thousand tons of mineral matter in solution
which it has taken from the land, and the Mississippi one hundred
and twelve million tons. Each carries away about four times as much
in suspension. The digestive or chemical power of water, then, is
only about one fourth as great as its mechanical power. Between the
two the land is made to pay heavy toll to the sea. But in time, in
geologic time, it all comes back. The suspended particles are
dropped and go to make up the sedimentary rocks, while the solutes
help cement the material of these rocks together, and also nourish
the sea life from which limestone and other organic rocks are made.
When these rocks are again lifted to the surface and disintegrated
into soil, then the debt of the sea to the land is paid. This
process, this cycle of soil loss and soil growth, has gone on
through all time, and must continue as long as the rain continues to
fall, or as long as the sea continues to send its tax-gatherers to
the land. In this great cycle of give and take of the elements, the
affairs of men cut but a momentary figure; how puny they are, how
transient! How the great changes, which in time amount to
revolutions, go on over our heads and under our feet, and we rarely
heed them, and are powerless to stay them! A summer shower carries
the soil of my side-hill, which is mainly disintegrated Silurian
rock and shale, into the river, and some millions of years hence,
when it has become stratified rock, and been lifted up into the
light of day, some other, and, I trust, wiser husbandman, will be
gathering his harvest from it, and be worried over the downpour that
robs him of it. The farmer's worry is bound to come back with the
soil, and be passed along with it.