g. Once more life takes
a long upward step in this little opossum-like animal, perhaps the
first creature whose young was born alive. These little creatures
called Microlestes or Dromatherium, of which only one or two different
but related species have been found in England and in North Carolina,
appear to have been insect-eaters of about the size and shape of the
Australian creature shown in Fig. 7. So far we know it in but few
specimens,--altogether only an ounce or two of bones,--but they are
very precious monuments of the past.

[Illustration: FIG. 6. DROMATHERIUM SYLVESTRE AND TEETH OF MICROLESTES
ANTIQUUS.]

In this Triassic time the climate appears to have been rather dry, for
in it we have many extensive deposits of salt formed by the
evaporation of closed lakes, of seas, such as are now forming on the
bottom of the Dead Sea, and the Great Salt Lake of Utah, and a hundred
or more other similar basins of the present day.

[Illustration: FIG. 7. MYRMECOBIUS.]

In the sea animals of this time we find many changes. Already some of
the giant lizard-like animals, which first took shape on the land, are
becoming swimming-animals. They changed their feet to paddles, which,
with the help of a flattened tail, force them through the water.

The fishes on which these great swimming lizards preyed are more like
the fishes of our present day than they were before. The trilobites
are gone, and of the crinoids only a remnant is left. Most of the
corals of the earlier days have disappeared, but the mollusks have not
changed more than they did at several different times in the earliest
stages of the earth's history.

[Illustration: FIG. 8. ICHTHYOSAURUS AND PLESIOSAURUS.]

After the Trias comes a long succession of ages in which the life of
the world is steadily advancing to higher and higher planes; but for a
long time there is no such startling change as that which came in the
passage from the coal series of rocks to the Trias. This long set of
periods is known to geologists as the age of reptiles. It is well
named, for the kindred of the lizards then had the control of the
land. There were then none of our large fish to dispute their control,
so they shaped themselves to suit all the occupations that could give
them a chance for a living. Some remained beasts of prey like our
alligators, but grew to larger size; some took to eating the plants,
and came to walk on their four legs as our ordinary beasts do, no
longer dr