luxuriant variety of forms from which the higher types may be selected.
This, it need hardly be said, is just what we find in the geological
record. The fruitful, steaming, rich-laden earth now offered tens of
millions of square miles of pasture to vegetal feeders; the waters, on
the other hand, teemed with gigantic sharks, huge Cephalopods, large
scorpion-like and lobster-like animals, and shoals of armour-plated,
hard-toothed fishes. Successive swarms of vegetarians--Worms, Molluscs,
etc.--followed the plant on to the land; and swarms of carnivores
followed the vegetarians, and assumed strange, new forms in adaptation
to land-life. The migration had probably proceeded throughout the
Devonian period, especially from the calmer shores of the inland seas.
By the middle of the Coal-forest period there was a very large and
varied animal population on the land. Like the plants, moreover,
these animals were of an intermediate and advancing nature. No bird or
butterfly yet flits from tree to tree; no mammal rears its young in the
shelter of the ferns. But among the swarming population are many types
that show a beginning of higher organisation, and there is a rich and
varied material provided for the coming selection.

The monarch of the Carboniferous forest is the Amphibian. In that age
of spreading swamps and "dim, watery woodlands," the stupid and sluggish
Amphibian finds his golden age, and, except perhaps the scorpion,
there is no other land animal competent to dispute his rule. Even the
scorpion, moreover, would not find the Carboniferous Amphibian very
vulnerable. We must not think of the smooth-skinned frogs and toads and
innocent newts which to-day represent the fallen race of the Amphibia.
They were then heavily armoured, powerfully armed, and sometimes as
large as alligators or young crocodiles. It is a characteristic of
advancing life that a new type of organism has its period of triumph,
grows to enormous proportions, and spreads into many different types,
until the next higher stage of life is reached, and it is dethroned by
the new-comers.

The first indication--apart from certain disputed impressions in the
Devonian--of the land-vertebrate is the footprint of an Amphibian on an
early Carboniferous mud-flat. Hardened by the sun, and then covered with
a fresh deposit when it sank beneath the waters, it remains to-day
to witness the arrival of the five-toed quadruped who was to rule the
earth. As the period pro