ature could
seize its prey, and yet use its feathered wings in flight. The small
head had jaws set with socketed teeth, like a reptile's, and the long,
lizard tail of twenty-one bones had a pair of side feathers at each
joint. This _Archeopteryx_ is the reptilian ancestor of birds. During
this age of the world, one branch of the reptile group established the
family line of birds. The bird-like reptiles are the connecting link
between the two races. How much both birds and reptiles have changed
from that ancient type, their common ancestor!

I have mentioned but a few of the types of animals that make the
reptilian age the wonder of all time. One after another skeletons are
unearthed and new species are found. The Connecticut River Valley, with
its red sandstones and shales of the Mesozoic Era, is famous among
geologists, because it preserves the tracks of reptiles, insects, and
crustaceans. These signs tell much of the life that existed when these
flakes of stone were sandy and muddy stretches Not many bones have been
found, however. The thickness of these rocks is between one and two
miles. The time required to accumulate so much sediment must have been
very great.

[Illustration: _By permission of the American Museum of Natural History_

Model of a three-horned Dinosaur, _Triceratops_, from Cretaceous of
Montana. Animal in life about 25 feet long]

[Illustration: _By permission of the American Museum of Natural History_

Mounting the forelegs of _Brontosaurus_, the aquatic Dinosaur]

It is not clear just what caused the race of giant reptiles to decline
and pass away. The climate did not materially change. Perhaps races grow
old, and ripe for death, after living long on the earth. It seems as if
their time was up; and the clumsy giants abdicated their reign, leaving
dominion over the sea, the air, and the land to those animals adapted to
take the places they were obliged to vacate.

THE AGE OF MAMMALS

The warm-blooded birds and mammals followed the reptiles. This does not
mean that all reptiles died, after having ruled the earth for thousands
of years. It means that changes in climate and other life conditions
were unfavourable to the giants of the cold-blooded races, and gradually
they passed away. They are represented now on the earth by lesser
reptiles, which live comfortably with the wild creatures of other
tribes, but which in no sense rule in the brute creation. They live
rather a lurking, caut