d the
Cambrian age opened upon the various fashions of armour that we there
described. But, although half the story of life is over, organisation
is still imperfect and sluggish. We have now to see how it advances to
higher levels, and how the drama is transferred from the ocean to a new
and more stimulating environment.

The Cambrian age begins with a vigorous move on the part of the land.
The seas roll back from the shores of the "lost Atlantis," and vast
regions are laid bare to the sun and the rains. In the bays and hollows
of the distant shores the animal survivors of the great upheaval adapt
themselves to their fresh homes and continue the struggle. But the
rivers and the waves are at work once more upon the land, and, as the
Cambrian age proceeds, the fringes of the continents are sheared, and
the shore-life steadily advances upon the low-lying land. By the end of
the Cambrian age a very large proportion of the land is covered with
a shallow sea, in which the debris of its surface is deposited. The
levelling continues through the next (Ordovician) period. Before its
close nearly the whole of the United States and the greater part of
Canada are under water, and the new land that had appeared on the site
of Europe is also for the most part submerged. The present British Isles
are almost reduced to a strip of north-eastern Ireland, the northern
extremity of Scotland, and large islands in the south-west and centre of
England.

We have already seen that these victories of the sea are just as
stimulating, in a different way, to animals as the victories of the
land. American geologists are tracing, in a very instructive way, the
effect on that early population of the encroachment of the sea. In each
arm of the sea is a distinctive fauna. Life is still very parochial; the
great cosmopolitans, the fishes, have not yet arrived. As the land is
revelled, the arms of the sea approach each other, and at last mingle
their waters and their populations, with stimulating effect. Provincial
characters are modified, and cosmopolitan characters increase in the
great central sea of America. The vast shallow waters provide a greatly
enlarged theatre for the life of the time, and it flourishes enormously.
Then, at the end of the Ordovician, the land begins to rise once more.
Whether it was due to a fresh shrinking of the crust, or to the simple
process we have described, or both, we need not attempt to determine;
but both in Europe an