It is most important to realize that changes are continually taking place on the surface of the earth. They are of three main kinds:
a) The wearing away of the land which we call denudation.
b) The removal of material from one part of the earth's crust to another, which we call transportation.
c) The laying down of this material in fresh places, which we call deposition.
The chief agents of denudation are the sun, wind, rain, frost, running water, moving ice and the sea.
Action of the sun. In hot countries the heat of the sun is very great during the day, and the rocks on the surface get very hot and expand or grow larger. This causes the rock to burst so that cracks form. Then at night time the rocks get very cold and contract. The cracks increase in size and gradually the rock breaks up into small pieces.
Wind The wind acts in two ways. Strong wind blows loose particles of soil and dust away. There is another way too, in which wind wears away the land. Strong wind armed with millions of sharp pieces of sand against a cliff or mass of hard rock, it gradually polishes the surface and begins to eat away the hard rock.
Rain. - The rain, especially in hot countries where there is a very heavy rainfall, has a powerful action. It loosens and carries away the soil. Rain, too, when it passes through the air, absorbs a considerable proportion of carbon dioxide gas. Rain water with this gas in solution is able to dissolve certain hard rocks such as limestone. Much of the rain water sinks into the ground and carries on its work of solution there, forming underground caves.
Frost. The action of the frost is important in cold countries. When the rain falls, part of it sinks into the ground and fills up cracks in the rocks. At night, when it gets very cold the water in the cracks freezes and expands which causes the cracks to widen. This goes on night till the crack becomes very wide, and one day when the ice melts a piece of rock breaks off.
Running water. When rain falls on to the ground some of it sinks in, but a great part of it collects together forming little streams which in their turn join up to form rivers. The streams cut for themselves little valleys, which at first are deep and narrow. The rain helps to wash away the banks, so that the valley becomes broader and broader. The force of the water itself is sufficient to do a great deal of damage, especially after a heavy storm when the stream is in flood but it is greatly increased by the load of stones and sand which the water collects; with their help the stream is able to cut its valley through solid masses of hard rock.
Moving ice. In very cold countries and high in the mountains where it is equally cold, instead of rivers we find solid masses of ice. These are glaciers. Like rivers they occupy valleys. This mass of ice moving downwards gradually scoops out its valley.
The sea. The sea is a powerful agent. It wears away the land especially in time of storm. Each wave hurls a great mass of water against the shore the shore and washes away the soft parts.
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Notes
to take place ,
at first
a great deal of ,
instead of , .
WORDS
crust
to realize ,
continually ,
main ,
to wear away (wore, worn) (),
denudation ,
removal ,
material
transportation ,
to lay down (laid, laid) ,
deposition ,
agent
frost
to act
action
rock ,
to expand ()
heat ,
to burst ,
crack
to contract (),
()
to increase , (),
()
size
to break up, off (broke, broken) (),
(),
to blow (away, against), (blew, blown) (, ,
, )
to loosen
loose ,
particle
soil
dust
to arm ()
sharp
cliff ,
considerable
to polish
to eat away (ate, eaten)
especially
powerful ,
to carry (on, away) (
)
to absorb ,
solution
to dissolve ()
certain ,
limestone
hard ,
to sink (sank, sunk) , (),
()
cave
to fall (fell, fallen) ,
to fill ,
to freeze
to melt
to collect ()
stream ,
to join up (),
()
valley
bank
force
sufficient
damage ,
flood
load
glacier
like
to scoop out ,
to hurl
I. Answer the following questions:
1. What kinds of changes are taking place in the earth's crust?
2. What is denudation?
3. What are the chief agents of denudation?
4. How does the sun affect the rocks?
5. When do rocks expand? contract?
6. What causes cracks in the rocks?
7. In what way does wind affect the rocks?
8. What is the action of the wind?
9. What does rain*water absorb from the air?
10. What is the chief agent of denudation in hot countries?
11. What causes the cracks to widen?
12. What happens with rain-water when it falls on to the ground?
13. What is the action of streams?
14. What causes the narrow valleys to become broader?
15. What increases the force of the water?
16. What are glaciers?
II. Find in the text equivalents to:
to understand, all the time, chief, to eat away, broad, to become, much, strong, to continue.
III. Translate into Russian paying attention to the translation of some verbs with different prepositions:
1. Rivers carry a load of sand and mud.
2. They carry on their work under hard conditions.
3. The rivers carry along stones and sand.
4. The wind loosens and carries away the soil.
5. Along the seashore the wind usually blows from the water toward the land during the day and from land toward water during the night.
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6. The wind blows away rock particles and rolls them along the surface of the earth.
7. When wind blows up the side of a mountain, it cools 3 degrees F. for every 1000 feet that it climbs.
8. The wind picks up sand and blows it against all uplifted surfaces.
TEXT 6
