THE WORK OF EROSION

The earth's crust is about 30 miles thick, but the rocks are not of the same thickness in all points of the earth which can be physically described as a ball of rock, partly covered by water and wrapped in an envelope of air. The crust of our earth undergoes slow but great alteration.

Erosion may be defined as the process of wearing away. As applied to geology, it signifies the wearing away of the rocks at the surface, chiefly by the action of streams or waves. Exposed rocks break up at the surface under the influence of heat and cold, frost and thaw, rain and wind, the roots of trees and plants, and the decomposing acids, chiefly derived from vegetation, which soak down into the rocks and attack them. The result is that such rocks crumble into sand and clay. Vegetation takes root, flourishes and dies, and new generations of plants arise; thus a top loam is formed, by the accumulation of vegetable remains. On account of its looseness, it usually moves downhill, into the valleys, and out towards the sea.

In mountains, running water wears deeply instead of widely, producing deep gorges and valleys in the solid rock. Between the gorges the rock remains as hills, even as mountains. Many mountains have this origin. The region which has been covered by glaciers shows a characteristic type of erosion, which has resulted in an irregular surface, with many lakes. There are many other peculiar types of erosion, produced in various ways, such as the fretting of rocks on the seashore by waves. In the desert, driving sand has also been responsible for erosion.

2. Виявити імпліцитні лексичні засоби.

3. Скласти міні-словник.

Контрольні питання

1. Що таке «імпліцитні лексичні засоби»?

2. Чому потрібно розкривати їх зміст?

3. Які є способи експлікації?

Література: [14, с. 217-219; 5, с. 79-84; 10, с. 68-75].