Geology. Козлова Е.П. - 46 стр.

              V Section V Texts for Supplementary Reading

                                         Our Earth
       Our whole earth is nothing more than a round, bumpy ball with a rock crust.
Much of the crust is covered by water, but underneath the oceans and seas, rivers and
lakes, there are rocks. Some of the ball is covered by great cities. The skyscrapers and
subways, paved streets and apartment buildings all rest on a deep layer of rocks.
       The green fields and tree-covered mountains, the mucky swamps and hot
deserts lie just above the rocky crust. Our soil from which plants grow is made of
rocks, and so the clothes we wear, the food we eat, the houses we live in, all began
with the rocks that form the hard outside of our whirling earth.
       The crust hasn't always been hard. At the very beginning the earth was just a
spinning mass of burning, smoking lava - the same kind of lava that sometimes hisses
and spits out of our active volcanoes. But gradually the outside began to stop burning
and smoking. It cooled off. As it cooled it hardened into the rocky crust. This
hardened lava formed the first rocks of the world, and you can see them every day
almost everywhere. They sometimes look quite slick and glassy, and sometimes you
can see the grains in them, with nearly perfect crystal forms running all through it.
       They are called "igneous". The word means "fire", and fire is certainly what
these rocks had been before they cooled and became hard.
       As the burning ball of the earth cooled, it didn't harden into anything very
smooth. There were great deep hollows in the round ball, and they filled with water.
It was a good thing it happened that way, too, for nothing can live without water.
       All around and about the hollow places that formed the great seas and oceans,
huge mountains of stone rose up. Wind and rain, ice and snow, began to beat down
on them and wear them down. Great boulders were carried from one place and put
into another. Rain and ice ground the rocks into fine dirt and sand, which filled up the
hollow places on the land, and settled in the bottoms of the rivers, lakes and seas. As
this sand and dirt piled layer on thick layer through the countless ages, it pressed into
hard rocks again. You can find them everywhere. They are usually made up of the
same kind of sand, sometimes brightly colored, and often there are pieces of plants or
even fossils to be found in them.
       These kinds of rocks are called "sedimentary" (sed-i-men-tary). That's because
any dust, dirt, or sand that settles is called "sediment".
       Hocks piled on top of other rocks, as the earth shifted and changed. The rocks
that were on the bottom were pressed down so that they didn't look like the same
rocks that they were before. If five heavy football players pile up in a heap, the poor
player on the bottom gets mashed and squeezed, and he doesn't look the same, either.
So it is with some rocks. They began as sedimentary or igneous ones, but heat and
water and time pressed them into another kind.
       There is a long word for these kinds of rocks. It is "metamorphic" (met-a-mor-
fick). The word means "change". You can find them, too, although they will be
harder to recognize than the others.


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