n the seas. But rarely
do we find any trace of the land life or even of the life that lived
along the shores. In this Carboniferous time, however, we have very
extensive sheets of rocks which were formed in swamps in the way shown
in the earlier part of this book. They constitute our coal-beds,
which, though much worn away by rain and sea, still cover a large part
of the land surface. These beds of coal grew in the air, and, although
the swamps where they were formed had very little animal life in them,
we find some fossils which tell us that the life of the land was
making great progress; there are new insects, including beetles,
cockroaches, spiders, and scorpions, and, what is far more important,
there are some air-breathing, back-boned animals, akin to the
salamanders and water-dogs of the present day. These were nearly as
large as alligators, and of much the same shape, but they were
probably born from the egg in the shape of tadpoles and lived for a
time in the water as our young frogs, toads, and salamanders do. This
is the first step upwards from the fishes to land vertebrates; and we
may well be interested in it, for it makes one most important advance
in creatures through whose lives our own existence became possible.
Still, these ancient woods of the coal period must have had little of
the life we now associate with the forests; there were still no birds,
no serpents, no true lizards, no suck-giving animals, no flowers, and
no fruits. These coal-period forests were sombre wastes of shade, with
no sound save those of the wind, the thunder, and the volcano, or of
the running streams and the waves on the shores.

In the seas of the Carboniferous time, we notice that the ancient life
of the earth is passing away. Many creatures, such as the trilobites,
die out, and many other forms such as the crinoids or sea lilies
become fewer in kind and of less importance. These marks of decay in
the marine life continue into the beds just after the Carboniferous,
known as the Permian, which are really the last stages of the
coal-bearing period.

When with the changing time we pass to the beds known as the Triassic,
which were made just after the close of the Carboniferous time, we
find the earth undergoing swift changes in its life. The moist climate
and low lands that caused the swamps to grow so rapidly have ceased to
be, and in their place we appear to have warm, dry air, and higher
lands.

On these lands of the Trias