|{ Quaternary | |
VI. | { Pliocene | Mammals | Early flowering
|{ Tertiary { Miocene | |
| { Eocene | |
V. | Mesozoic | Reptiles | Cycads
IV. | Carboniferous | Amphibians| Ferns and Conifers
III. | Devonian | Fishes | Ferns
II. | Silurian | Molluscs | Seaweeds
I. | Fire-formed | No life | No life
------+----------------------+-----------+-----------------------

It is by dying that the creatures of the sea write their epitaphs. The
mud or sand swallows them up. In time these submerged banks may be left
dry, and become beds of stone. Then some of the skeletons and shells
may be revealed in blocks of quarried stone, still perfect in form after
lying buried for thousands of years.

The leaves of this great stone book are the layers of rock, laid down
under water. Between the leaves are pressed specimens--fossils of
animals and plants that have lived on the earth.

THE FOSSIL FISH

I remember seeing a flat piece of stone on a library table, with the
skeleton of a fish distinctly raised on one surface. The friend who
owned this strange-looking specimen told me that she found it in a stone
quarry. She brought home a large piece of the slate, and a stone-mason
cut out the block with the fish in it, and her souvenir made a useful
and interesting paper-weight.

The story of that fish I heard with wonder, and have never forgotten. I
had never heard of fossil animals or plants until my good neighbour
talked about them. She showed me bits of stone with fern leaves pressed
into them. One piece of hard limestone was as full of little sea-shells
as it could possibly be. One ball of marble was a honeycombed pattern,
and called "fossil coral."

The fossil fish was once alive, swimming in the sea, and feeding on the
things it liked to eat, as all happy fishes do. Near shore a river
poured its muddy water into the sea, and the sandy bottom was covered
with the mud that settled on it. At last the fish grew old, and perhaps
a trifle stupid about catching minnows. It died, and sank to the muddy
floor of the sea. Its horny bones were not dissolved by the water. They
remained, and the mud filtered in and filled all the spaces. Soon the
fish was buried completely by the sediment the river brought.

Years, thousands of them, went by, and the layer of mud was so t