ne of the many features which I have indicated as pointing to a former
fluidity of the earth may be explained here. We shall see in the course
of this work that the mountain chains and other great irregularities of
the earth's surface appear at a late stage in its development. Even
as we find them to-day, they are seen to be merely slight ridges and
furrows on the face of the globe, when we reflect on its enormous
diameter, but there is good reason to think that in the beginning the
earth was much nearer to a perfectly globular form. This points to
a liquid or gaseous condition at one time, and the flattening of the
sphere at the poles confirms the impression. We should hardly expect
so perfect a rotundity in a body formed by the cool accretion of solid
fragments and particles. It is just what we should expect in a fluid
body, and the later irregularities of the surface are accounted for by
the constant crumpling and wearing of its solid crust. Many would find
a confirmation of this in the phenomena of volcanoes, geysers, and
earthquakes, and the increase of the temperature as we descend the
crust. But the interior condition of the earth, and the nature of these
phenomena, are much disputed at present, and it is better not to rely on
any theory of them. It is suggested that radium may be responsible for
this subterraneous heat.

The next stage in the formation of the earth is necessarily one that we
can reach only by conjecture. Over the globe of molten fire the vapours
and gases would be suspended like a heavy canopy, as we find in Jupiter
and Saturn to-day. When the period of maximum heat production was
passed, however, the radiation into space would cause a lowering of
the temperature, and a scum would form on the molten surface. As may be
observed on the surface of any cooling vessel of fluid, the scum would
stretch and crack; the skin would, so to say, prove too small for the
body. The molten ocean below would surge through the crust, and bury it
under floods of lava. Some hold that the slabs would sink in the ocean
of metal, and thus the earth would first solidify in its deeper layers.
There would, in any case, be an age-long struggle between the molten
mass and the confining crust, until at length--to employ the old Roman
conception of the activity of Etna--the giant was imprisoned below the
heavy roof of rock.

Here again we seem to find evidence of the general correctness of the
theory. The objection has been