1. In a former chapter on Geology, we spoke of the various causes that have altered or modified the appearance of the earth's surface, and of the formation, by the action of water, of the stratified rocks. Now, if we examine carefully the substance of these rocks, we find scattered here and there amongst them certain organic bodies, which, although now petrified, certainly had, at one time, an animal or vegetable origin. To these substances the term fossil has been given, a word derived from the Latin word fossus (dug up).

2. If we ask ourselves by what process these bodies have become encased with stone, how it is that in the solid parts of hard rocks, delicate shells, well marked and defined leaves, flowers and fruits, impressions of raindrops, footprints of birds, entire

and perfect skeletons of fishes, reptiles, and land animals (found in some places, as in coal mines, hundreds of feet below the present level of the surface) should be found, we must look to what is actually taking place at the present day for an explanation.

3. If we visit an estuary of a large river, we generally find large banks of mud and silt. These are the washings of the river from the banks, of the basin which it drains. In times of floods immense quantities of matter are brought down, and the water assumes the muddy or clayey colour of the soil of the district. The water also brings down dead fish, shells, insects, land animals which have been drowned, trees, fruits, and flowers. At the mouth of the river the water loses its velocity, and begins to settle down, and the animal and vegetable remains, floating about in it, are gently buried in the soft silt or mud.

4. In the course of ages, perhaps, a new river bed is formed, or the estuary becomes elevated, and the soft mud with its animal and vegetable matter, impregnated with lime, iron, and other substances held in solution by the water, becomes consolidated into hard strata or stone, and will give information to generations yet to come, of the species of the animal and vegetable kingdom that exist at the present day.

5. To the geologist a stone quarry is like an open page of the world's book, and the fossils scattered hither and thither about the rocks are the symbols, or letters, that speak to him of the world's history

ages before. They tell him the climate that existed in the place when the rocks were first laid down, the kinds of fishes that inhabited the seas, the plants that grew on the land, and the animals that roamed amongst them. They even give him the date (though not in years, but in epochs of time) when the rocks (in comparison with others) were laid down.

6. Geologists, by examining carefully, and comparing the fossils found in the various stratified rocks with each other, have been enabled to arrange the strata into various systems, and very wonderful and important information has been gained of the various changes that have taken place in animal and vegetable life at different epochs. By means of fossils, geologists have ascertained that very great changes have taken place in the climate of this country. At one epoch it was arctic in character, large glaciers filled the mountain valleys of Wales and Scotland, and immense icebergs floated down the seas and deposited masses of rocks from Wales and Cumberland in the sandy bottom of an ocean, whose bed now forms part of the midland counties of England.

7. At another period a humid semi-tropical climate prevailed, and huge tree ferns and tall reeds covered the wide morasses of the land, and formed the vast accumulations of vegetable matter that have, in the course of ages, been consolidated into the coal measures.

8. At another time the climate was tropical; large herds of elephants roamed over the plains,

and huge lions and cave bears inhabited the limestone districts of Devon and Derbyshire.

9. Lastly came the temperate climate that exists at the present day, and in the peat mosses and

recent river deposits we find the fossils to be those of animals and vegetables very similar in structure to those that live at the present time.

10. The study of geology, indeed, opens up a vast

field of thought, and is one of the most healthgiving of all sciences. Only a small outlay is required; a text-book, a hammer and a bag to carry the specimens. With these the collector can wander into the quarries, the mountain glens, and under the sea cliffs, and add health to his body, and culture to his mind.

A. C.

LESSON XLI.

ANIMAL LIFE.

1. Living bodies are usually divided into the animal and vegetable kingdoms. It may seem at first sufficiently easy to make the distinction between an animal and a plant; and, as long as we confine our views to the higher orders of animated beings, there is no room for doubt.

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2. But when we descend in the scale to the radiated animals, which present no distinct nervous system, no organs of sensation, no observable mode of communication with the external world; it then becomes necessary to inquire more accurately into the peculiar points, which should decide us to arrange them under the one class, or the other.

3. Perhaps the most certain of these, is the presence of a digestive organ. Cuvier2 mentions three other marks of distinction, which, however, are by no means so general. They are, the presence of nitrogen, the existence of a circulation, and respiration.

4. Nitrogen, it is true, exists in all animal bodies, but all vegetables, likewise, contain it, and some in