What type of creatures do they meet?

The
travelers, en route to the center of the earth, see exotic creatures not found on the surface of
the planet. For example, they view living dinosaurs, such as an Ichthyosaurus and a Plesiosaurus
having a fight. They also see very large insects and mastodons. In fact, they come across a
whole herd of mastodons, exactly like those discovered as fossils in Ohio in 1801.

They also see a very large man who is perhaps twelve feet tall. He has a head the size
of a buffalo head and lots of matted hair. The voyagers are not entirely sure if he is a man, an
ape-man, or some member of the monkey family, but they avoid having any contact with
him.

They also find the plant life of the earth's surface all jumbled
together:

there appeared confounded together and
intermixed, the trees of such varied lands, specimens of the vegetation of every part of the
globe; there was the oak near the palm tree, the Australian eucalyptus, an interesting class of
the order Myrtaceaeleaning against the tall Norwegian pine, the poplar of the north, mixing its
branches with those of the New Zealand kauris.