y of this argument will be recognized, perhaps, only by those
naturalists to whom the Animal Kingdom has begun to appear as a
connected whole. For those who do not see order in Nature it can have
no value.

[Illustration: FOSSILS OF TRIASSIC VEGETATION.]

[Illustration: BIRD OF THE JURASSIC PERIOD.(The Oldest Bird.)]

[Illustration: SKELETON OF BIRD OF THE CRETACEOUS PERIOD.]

[Illustration: SKELETON OF ANIMAL OF THE EOCENE PERIOD.]

For a table containing the geological periods in their succession, I
would refer to any modern text-book of Geology, or to an article in
the _Atlantic Monthly_ for March, 1862, upon "Methods of Study in
Natural History," where they are given in connection with the order of
introduction of animals upon earth.

Were these sets of rocks found always in the regular sequence in which
I have enumerated them, their relative age would be easily
determined, for their superposition would tell the whole story: the
lowest would, of course, be the oldest, and we might follow without
difficulty the ascending series, till we reached the youngest and
uppermost deposits. But their succession has been broken up by
frequent and violent alterations in the configuration of the globe.
Land and water have changed their level,--islands have been
transformed to continents,--sea-bottoms have become dry land, and dry
land has sunk to form sea-bottoms,--Alps and Himalayas, Pyrenees and
Apennines, Alleghanies and Rocky Mountains, have had their stormy
birthdays since many of these beds have been piled one above another,
and there are but few spots on the earth's surface where any number of
them may be found in their original order and natural position. When
we remember that Europe, which lies before us on the map as a
continent, was once an archipelago of islands,--that, where the
Pyrenees raise their rocky barrier between France and Spain, the
waters of the Mediterranean and Atlantic met,--that, where the British
Channel flows, dry land united England and France, and Nature in those
days made one country of the lands parted since by enmities deeper
than the waters that run between,--when we remember, in short, all the
fearful convulsions that have torn asunder the surface of the earth,
as if her rocky record had indeed been written on paper, we shall find
a new evidence of the intellectual unity which holds together the
whole physical history of the globe in the fact that through all the
storms of time the inve