the land there
stalked huge reptiles fifty and sixty feet long, and, when standing
erect, at least thirty feet high.<15> Some of these huge creatures
were carnivorous, living on other animals. Others fed on the foliage of
trees. In the air, huge reptilian bats, veritable flying dragons with
a spread of wings from ten to twenty feet, disported themselves.<16>
In the sea there swam great reptilian whales, seals, and walruses.<17>
There was a marvelous abundance of reptilian life. At the present day,
there are not more than six species of reptiles in the whole world
having a length of over fifteen feet, and not more than eighteen
species exceeding ten feet in length. But from one limited locality,
representing but one era of this age in England, there have been
discovered four or five species of carnivorous reptiles twenty to fifty
feet long, ten or twelve species of crocodiles, lizards, and swimming
reptiles from ten to sixty feet long--besides multitudes of great flying
reptiles and turtles. Doubtless similar scenes of animal life were
everywhere represented.

Illustration of The Labyrinthodon.--------

Birds made their first appearance during the Mesozoic time, and here we
obtain a clear view of nature's methods of work. There is no longer a
doubt but that the first birds were simply modified reptiles. The first
bird had a long jointed tail, and a bill well supplied with formidable
teeth.<18> It was during this period that the first representative of
the class Mammalia, to which man belongs, appears.<19> It is in the
rocks of this era that we meet with remains of marsupials, the order to
which opossums belong. This is the lowest of the Mammalian class. To the
class Mammalia belong the most highly organized animals. They have been
the ruling animals since the close of Mesozoic time. We must now watch
their development with especial care. For this brief review, as far as
it has gone, has shown a steady and gradual progress in life forms, the
lower invariably preceding the higher. We therefore feel that it will be
vain to seek for any trace of man until we find undoubted proofs of the
existence of all the forms of animals below him. The last great division
of time is called Cenozoic.<20> This means new life forms. In this age,
the forms of life are much nearer our own. As it was some time during
this epoch when man makes his appearance, we deem it best to go into
more detail, and give the subdivisions of this period. It