le
confidence. As we go deeper into the rocks and find older fossils, the
evidence becomes less certain. The animals differed enough from those
of to-day for us to be less sure what they were like. As we keep on
moving backward through time, and downward through the rocks, we find,
after a while, strata in which there are evidences of life that
existed long ago, but in which these traces are so altered that it is
impossible to tell what sort of living things existed; we learn only
that they were alive. Going back still further, these fade out. There
is no knowing when the earth began; there is no knowing when life
began upon the earth. It is not meant that men have not wondered, even
reckoned carefully, as to how long ago each of these events occurred.
Many speculations have proved entirely useless, a few remain as yet
neither confirmed nor disproved, and of such we shall speak.

For the last hundred years the theory of the earth's origin suggested
by the Marquis Pierre Simon De La Place, of France, near the end of
the eighteenth century, has held almost undisputed sway among men who
were willing to consider the question as open to human solution. This
theory is known as La Place's Nebular Hypothesis. When men began to
study the heavenly bodies with the newly invented telescope, new ideas
naturally sprang up. Among the objects which the glass disclosed were
the nebulae, which are great clouds of fire mist, glowing masses of
gas. They are scarcely visible to the naked eye, but are among the
most interesting objects in the heavens when seen through a telescope.
The other suggestive heavenly body was our sister planet, Saturn.
Besides having a full complement of moons, Saturn has around it, as
distant as we would expect moons to be, three great rings. These look
very much as if one's hat, with an enormously wide brim, should have
the connection between the rim and the hat broken out completely, but
the rim should still float around the hat without touching it and
should steadily revolve as it stood there. The rings of Saturn are not
solid like the suggested hat rim. They are evidently made up of a
great number of very small particles, each moving around the center of
Saturn. But the great cloud of them is spread out flat. At the
distance which Saturn is from the earth they look as if they made a
solid sheet. Furthermore, they do not form, as it were, one continuous
hat rim, but it is as if the rim were broken into three ci