e composed of their remains show that vast areas of the
sea-floor must have been covered with groves of sea-lilies, bending on
their long, flexible stalks and waving their great flower-like arms in
the water to attract food. With them there is now a new experiment in
the stalked Echinoderm, the Blastoid, an armless type; but it seems to
have been a failure. Sea-urchins are now found in the deposits,
and, although their remains are not common, we may conclude that the
star-fishes were scattered over the floor of the sea.

For the rest we need only observe that progress and rich diversity of
forms characterise the other groups of animals. The Corals now form
great reefs, and the finer Corals are gaining upon the coarser. The
Foraminifers (the chalk-shelled, one-celled animals) begin to form thick
rocks with their dead skeletons; the Radiolaria (the flinty-shelled
microbes) are so abundant that more than twenty genera of them have been
distinguished in Cornwall and Devonshire. The Brachiopods and Molluscs
still abound, but the Molluscs begin to outnumber the lower type of
shell-fish. In the Cephalopods we find an increasing complication of the
structure of the great spiral-shelled types.

Such is the life of the Carboniferous period. The world rejoices in a
tropical luxuriance. Semi-tropical vegetation is found in Spitzbergen
and the Antarctic, as well as in North Europe, Asia, and America, and in
Australasia; corals and sea-lilies flourish at any part of the earth's
surface. Warm, dank, low-lying lands, bathed by warm oceans and steeped
in their vapours, are the picture suggested--as we shall see more
closely--to the minds of all geologists. In those happy conditions the
primitive life of the earth erupts into an abundance and variety that
are fitly illustrated in the well-preserved vegetation of the forest.
And when the earth has at length flooded its surface with this seething
tide of life; when the air is filled with a thousand species of insects,
and the forest-floor feels the heavy tread of the giant salamander and
the light feet of spiders, scorpions, centipedes, and snails, and the
lagoons and shores teem with animals, the Golden Age begins to close,
and all the semi-tropical luxuriance is banished. A great doom is
pronounced on the swarming life of the Coal-forest period, and from
every hundred species of its animals and plants only two or three will
survive the searching test.

CHAPTER X. THE PERMIAN REVOLU