there are sunken places that are broad and long. I suppose you never took so much interest in the wrinkled skin of a dried-up apple before, did you? Well, I want you to look at this for some time carefully, and think about it a great deal.

The earth is somewhat the shape of an apple. It has a covering. This covering, you have learned, is thick and hard, being made up of layers of rock. In some places the covering is thicker than it is in other places.

Now it is known that the earth is growing smaller because it is constantly giving off heat into the air. As it becomes smaller, the crust or covering wrinkles to suit or fit the inside, just as the apple skin wrinkles to fit the smaller size of the apple. You think the hard stone of the earth's surface would not break, but it does. It breaks because it is so heavy, and because its support has shrunken away from it. Wherever it breaks or wrinkles down, the surface of the earth may be shaken or moved about for many miles in many directions. When this happens, we call it an earthquake. So you see the breaking or wrinkling of the earth causes the earthquake. An earthquake, then, is caused because the earth's surface has broken away somewhere or wrinkled.

It happens sometimes when there are earthquakes that great openings are made in the earth's crust. Through these openings pour forth streams of ashes and of melted rock called lava. The ashes, after being thrown high into the air, fall about the openings, and form mountains. These are called volcanoes. Have you not seen many pictures of volcanoes? Did you ever see a real volcano?

The lava often bursts through the ashes, and spreads out in broad sheets over the surrounding land, filling the spaces between the upturned rocks and extending for miles and miles in every direction.

This is another kind of geologic formation, for the space covered by the lava from a volcano may be as large or larger than the lake of which you have read in another lesson. Should earthquakes again come, this formation might be broken and tilted into mountain ranges and long lines of hills

with valleys between them. The rocky layers and the lava layer might thus lie in great confusion, one upon the other. There are many volcanic formations in our own country. You will learn where they are some day, when you study geography.

8. HOW SOIL IS MADE.

Many years ago, centuries perhaps, there was no soil or ground as you call it, where you now see fertile farms and beautiful green meadows.

In its stead there may have been a rocky ledge many miles long and many feet deep on which the sun shone and the rain fell year after year.

This is what happens.

Exposure to the air and the rain in the course of time causes the rock to decay slightly, so that when little wandering seeds of tiny plants, carried by the wind, fall upon it, they are able to lodge in its crevices or cracks. There they begin to grow.

When they die, the rain, in soaking through them, creates various acids which soften still more of the rock.

This constant decay in time forms a kind of soil or beginning for the growth of vegetation. The roots of these plants and trees, making their way into the fissures of the rock, often force its particles aside, breaking it into pieces. These pieces decay a great deal more rapidly than when they were a part of the larger mass, because more surface is exposed to the air and the rain.

Jack Frost also plays a prominent part in soilmaking. The rain, sinking through the thin layer

of soil, penetrates the pores of the rock, where in winter it freezes. In freezing it expands and pushes aside the particles of rock and breaks it into little fragments.

Grasses and creeping vines soon take root there, and dying, make room for other and larger plants. Now, after long years, we find large plants, shrubs, and even forest trees growing where there was once but a layer of rock.

The floods of spring come. The water, forever seeking an outlet, cuts for itself channels in the mountain sides and in the plains. Thus brooks and rivers begin.

The water, on its way to and through, the brooks and rivers, carries the new-crumbled rock or the new-made soil along with it and deposits. it in the plains below. Thus, soil is made, and covers the beautiful valleys through which wind creeks and rivers.

THE SOIL OF RIVER VALLEYS.

After a rainfall you have often seen the water flowing down the gutters, carrying with it the pebbles, sand, and mud, which spread out in a thin sheet along the sides and at the foot of the gutter.

Imagining this gutter a river, we can readily see