Changes in the earth's crust

It is most important to realize that changes are continually taking place on the surface of the earth. They are of three main kinds:

1. The wearing away of the land which we call denudation.

1. The removal of material from one part of the earth's crust to another, which we call transportation.

2. 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.

Notes

to take place – иметь место, происходить

at first – сначала

a great deal of – много, значительное количество

instead of – вместо того, чтобы.

WORDS

crust земная кора

to realize понимать,

ясно представлять себе

continually постоянно, непрерывно

main главный, основной

to wear away (wore, worn) стирать(ся), выветриваться

denudation обнажение, денудация

removal удаление,

перемещение

material материал

transportation транспортировка,

перенос

to lay down (laid, laid) класть, отлагать

deposition отложение, осадок

agent агент

frost мороз

to act действовать

action действие

rock скала, горная порода

to expand расширять(ся)

heat тепло, теплота

to burst ломаться, разрываться

crack трещина

to contract сокращать(ся),

сжимать(ся)

to increase расти, увеличивать(ся),

повашать(ся)

size размер

to break up, off (broke, broken) ломать(ся),

разбивать(ся),

отламываться

to blow (away, against), (blew, blown) дуть (сдувать, развевать,

бить о, ударять о)

to loosen разрыхлять

loose свободный, рыхлый

particle частица

soil почва

dust пыль

to arm вооружать(ся)

sharp острый

cliff утес, скала

considerable значительный

to polish шлифовать

to eat away (ate, eaten) разрушать

especially особенно

powerful сильный, могучий

to carry (on, away) нести (продолжать

уносить)

to absorb поглощать, впитывать

solution раствор

to dissolve растворять(ся)

certain определенный,

некоторый

limestone известняк

hard твердый, трудный

to sink (sank, sunk) тонуть, погружать(ся),

опускать(ся)

cave пещера

to fall (fell, fallen) падать, выпадать

to fill наполнять, заполнять

to freeze замерзать

to melt таять

to collect собирать(ся)

stream река, ручей

to join up соединять(ся),

объединять(ся)

valley долина

bank берег реки

force сила

sufficient достаточный

damage вред, ущерб

flood половодье

load груз

glacier ледник

like подобно

to scoop out вычерпывать,

вырывать

to hurl бросать