Table of Contents
| Part | Rock Systems | Dominant Animals | Dominant Plants | |||
| VII. | Recent | Man | Flowering kinds | |||
| { | 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 thick and heavy above the skeleton of the fish that it bore a weight of tons there, under the water. The close-packed mud became a stiff clay. After more thousands of years, the sea no longer came so far ashore, for the river had built up a great delta of land out of mud. The clay in which the fish was hidden hardened into slate. Water crept down in the loose upper layers, dissolving out salt and other minerals, and having harder work to soak through, the lower it went. The water left some of the minerals it had accumulated, calcium and silica and iron, in the lower rock beds, making them harder than they were before, and heavier and less porous.