us, while the differences between the living
creatures of the time before the chalk and those of the present day
appear startling, if placed side by side, we are led from one to the
other by the most gradual progress, if we follow the course of Nature
through the whole series of those relics of her operations which she
has left behind.

[Illustration: SKELETON OF THE PTERODACTYL.]

And it is by the population of the chalk sea that the ancient and the
modern inhabitants of the world are most completely connected. The
groups which are dying out flourish, side by side, with the groups
which are now the dominant forms of life.

Thus the chalk contains remains of those flying and swimming
reptiles, the pterodactyl, the ichthyosaurus, and the plesiosaurus,
which are found in no later deposits, but abounded in preceding ages.
The chambered shells called ammonites and belemnites, which are so
characteristic of the period preceding the cretaceous, in like manner
die with it.

[Illustration: THE SKELETON OF THE ICHTHYOSAURUS.]

[Illustration: THE SKELETON OF THE PLESIOSAURUS.]

[Illustration: AMMONITES.]

But, among these fading remainders of a previous state of things, are
some very modern forms of life, looking like Yankee peddlers among a
tribe of red Indians. Crocodiles of modern type appear; bony fishes,
many of them very similar to existing species, almost supplant the
forms of fish which predominate in more ancient seas; and many kinds
of living shell-fish first become known to us in the chalk. The
vegetation acquires a modern aspect. A few living animals are not even
distinguishable as species from those which existed at that remote
epoch. The Globigerina of the present day, for example, is not
different specifically from that of the chalk; and the same may be
said of many other Foraminifera. I think it probable that critical and
unprejudiced examination will show that more than one species of much
higher animals have had a similar longevity; but the only example
which I can at present give confidently is the snake's-head lamp-shell
(_Terebratulina caput serpentis_), which lives in our English seas and
abounded (as _Terebratulina striata_ of authors) in the chalk.

[Illustration: BELEMNITES.]

[Illustration: TEREBRATULINA.]

The longest line of human ancestry must hide its diminished head
before the pedigree of this insignificant shell-fish. We Englishmen
are proud to have an ancestor who was present at the B