furnished its green sprout,
and died if it found no nourishment.

All the hundreds of acorns rolled down the slopes, Not one rolled up;
and here was a _law_,--the law of gravitation,--in full activity.
There were scores of other laws active, too; for evolution had gone a
long way when we had an earth fit to be lived on, and hills in their
present shape, and a tree bearing acorns that would reproduce their
kind. But ever since the fiery mist this simple law of gravitation has
been acting, binding the whole universe together, making a
relationship between each clod and every other clod, and forcing
every stone, every acorn, and every rain-drop to move down and not up.

Just as this law operates,--continuously, silently, inexorably,--so
every other law makes itself felt in its own sphere. Gravitation is
simple. The law according to which an acorn makes an oak--and not a
pine-tree is complex. But the laws of Nature are all alike, and if we
understand the simple ones, we can at least partly comprehend the more
complex. They are nothing but fixed habits on a large scale.

So the acorns fell year by year and sprouted; and one out of a
thousand found good soil, and was not wasted, and made a tree. And so
all around (below) the tree with which we started there grew a grove
of oaks like it, in fact its children; and finally the original trees
died, but not without having left successors.

First of all, the green hillside is smooth and untrodden. There is
nothing but grass and flowers, borne there by the winds, which leave
no track. There is no animal life even in this secluded spot save the
birds, and they too leave no track. By and by there comes a hard
winter, or a dearth of food, and a pair of stray squirrels emigrate
from their home in the valley below; and the history of our hill and
its woods begins. Mere chance decides the choice of the particular
oak-tree in which the squirrels make their home. From the foot of this
tree they make excursions here and there for their store of winter
food,--acorns and the like,--and they leave little paths on the
hillside from tree to tree.

The best-marked paths run to the places where there are the most
acorns. A little later on there are more squirrels in the colony,--the
young of the parent pair, and other colonists from the valley. The
little tracks become plainer and plainer.

Later still come other wild animals in search of food,--squirrels will
do. The wild animals do not rem