ormidable tusk, is represented in the subjoined wood-cut.

[Illustration]

Its hanging lower jaw, with the protruding tusk, corresponds perfectly
to the formation of the lower jaw and teeth in the Manatee. Some
resemblance of the Dinotherium to the Mastodon suggested a comparison
with that animal as the next step in the investigation, when it was
found that at the edge of the lower jaw of the latter there was a pit
with a small projecting tooth, also corresponding exactly in its
position to the tusk in the Dinotherium. The Elephant was now examined;
and in him also a rudimentary tooth appeared in the lower jaw, not cut
through, but placed in the same relation to the jaw and the other teeth
as that of the Mastodon. It would seem, then, that the Manatee makes one
in this series of Dinotherium, Mastodon, and Elephant, and represents
the aquatic Pachyderms, occupying the same relation to the terrestrial
Pachyderms as the Seals bear to the terrestrial Carnivora, and, like
them, lowest in structure among their kind.

The announcement of Cuvier's results stimulated research, and from this
time forward Tertiary Mammalia became the subject of extensive and most
important investigations among naturalists. The attention of collectors
once drawn to these remains, they were found in such numbers that the
wonder was how they had been so long hidden from the observation of men.
They remind us chiefly of tropical animals; indeed, Tigers, Hyenas,
Rhinoceroses, Hippopotamuses, Mastodons, and Elephants had their home in
countries which now belong to the Cold Temperate Zone, showing that the
climate in these latitudes was much milder then than it is at present.
Bones of many of these animals were found in caverns in Germany, France,
Italy, and England. Perhaps the story of Kirkdale Cave, where the first
important discovery of this kind was made on English soil, may not be so
well known to American readers as to forbid its repetition here.

It was in the summer of 1821 that some workmen, employed in quarrying
stone upon the slope of a limestone hill at Kirkdale, in Yorkshire, came
accidentally upon the mouth of a cavern. Overgrown with grass and
bushes, the mouth of this cave in the hill-side had been effectually
closed against all intruders, and it was not strange that its existence
had never been suspected. The hole was small, but large enough to admit
a man on his hands and knees; and the workmen, creeping in through the
opening, foun