38. Подготовьте сообщение на тему:

Different types of coals and their comparison with each other (for example, lignite and anthracite or anthracite and brown coal, etc.), their carbon content, heat value, liability to spontaneous combustion and the use of each grade of coal.

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39. Расскажите, что вы знаете об угольных пластах (рис. 3 и 4). В своем рассказе дайте ответы на следующие вопросы:

1. What do Figures 3 and 4 show?

2. What figure shows the seam which consists only of coal bands?

3. Is the coal seam (Fig. 3) horizontal or inclined?

4. Is the shape of the seam typical of igneous rocks or sedimen­ tary rocks? What do you know about the structure of sedimentary rocks?

5. Can you explain why the coal seam shown in Fig. 4 is called complex? What does the seam consist of?

6. What mineral substances may separate coal beds? What do we call them?

7. What is thicker, coal bands or rock partings?

40. Прочитайте текст в и кратко передайте его содержание по-русски.

ТЕКСТ В

l.For along time coal has been the principal fuel, the main source of thermal and electric energy. Now it continues to play an important part in the economy.

2. Coal is the product of vegetable matter that has been formed from the remains of plants and animals accumulated in swamp areas millions of years ago. Although some coals were deposited 4,000,000,000 years ago during the Silurian period, most coals were formed during the Upper and Lower Carboniferous geological epochs about 250,000,000 years ago.

3. Coal formation processes are similar to those of sedimentary rocks. Various coal seams can be studied and related geologically to the sedimentary rocks with which they are associated. Coal contains varying amounts of carbon and volatile material as well as impurities such as sulphur, phosphorus, incombustible rock material and moisture.

4. The physical characteristics of coal concern the structural aspects of the coal bed and texture. Structurally coal beds are charac­ terized by the same irregularities in thickness, uniformity and continuity as other strata of sedimentary origin. Thickness varies greatly. Coal beds may consist of essentially uniform continuous

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strata or like other sedimentary deposits may be made up of bands or benches of varying thickness. The benches may be separated by thin layers of clay, shale, pyrite or other mineral matter, commonly called partings. Like other sedimentary rocks coal beds may be structurally disturbed by folding and faulting.

5. Many classifications of coal have been suggested: by geologic age, coking properties, commercial application and chemical composition.

6. There exist four main types of coal: anthracite, bituminous, subbituminous, lignite and brown coal. When speaking about the classification of coal based on its nature as rock mineral, scientists distinguish (различать) the following rock varieties or lithotypes such as vitrain, clarain, durain and fiisain. These are the four constituents (составная часть) of coal.

7. Although the utilization of coal varies widely with rank, three general fields of coal utilization may be distinguished. They are combustion (domestic, industrial, railroads and public utilization), gasification and carbonification (high-temperature coke for metallurgical uses and low-temperature coke for producing smokeless fuel).