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The Earth’s crust is largely made up of rocks. Most of rocks are homogeneous but some are heterogeneous aggregates.

Rocks never occur in the form of layers or irregular masses of different sizes and shapes. Three types of rocks are recognized according to their composition: igneous, sedimentary and metamorphic.

It is believed that at one time the Earth was solid. Any material which was formed from solid rock is referred to as igneous rock.

During the long history igneous rocks were eroded. The eroded particles were set down in layers and subjected to high pressure. Thus, sedimentary rocks were formed.

Although sedimentary and igneous rocks were subjected to pressure and heat their original qualities were never changed. As a result, new materials known as metamorphic rocks were formed.

Ex.5.

Вставьте нужные предлоги.

1. All rocks are composed … minerals.

2. Minerals are … great interest and importance … the geologists.

3. The oceanic crust is made up … dark rocks.

4. Any material which was formed … liquid rock is called igneous rock.

5. This area is now covered … sedimentary rock.

6. … one time the Earth was liquid.

7. … time, some of these materials were subjected … heat.

8. The word “metamorphic” comes … two Greek words.

Ex.6.

Прочитайте текст и определите какие из приведенных ниже высказываний соответствуют его содержанию.

The topmost layers of the earth are called the crust. Its thickness and composition are not constant, but vary between the continental crust and the oceanic crust. The former is much thicker than the latter and consists of light rocks; the latter is made up of dark rocks.

1) The uppermost layers of the Earth are referred to as the crust. (…)

2) The composition of the crust is permanent. (…)

3) The thickness of the crust does not change. (…)

4) There are two types of the crust: oceanic and continental. (…)

5) The continental and the oceanic crust differ in colour and in thickness. (…)

6) The oceanic crust is much thicker than the continental one. (…)

7) The oceanic crust consists of dark rocks. (…)

Ex.7.