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22. Переведите наречия, образованные от прилагательных с помощью суффикса -1у.

chief главный — chiefly ..., general общий, основной — gener­ally ..., common общий — commonly ..., original первоначальный — originally ..., particular особенный — particularly ..., practical практический, фактический — practically ..., usual обычный — usually ..., wide широкий — widely ...

23. Прочитайте следующие сочетавм слов. Переведите их:

cleavage distribution the definition of rocks

geological disturbances schistose structure

schistose coal low-grade metals

medium-grade coals high-grade oil the most common metamorphic exposed igneous rocks

rocks single oithoclase crystals

chemically active fluids scientific value

rock pressure water pressure

excess of water thin sheets

foliated and non-foliated the Earth's surface

metamorphic rocks separate plates

24. Определите значения выделенных слов по сходству их корней с соответствующих слов в русском языке:

metamorphic rocks; some changes in texture; in mineral com­position and structure; the description of metamorphism; schistose structure; the role of water; four variable geologically related pa­rameters; flaky materials; the mechanism of metamorphic deforma­tion; crystalline schists; the great dislocations of the Earth's crust; during normal progressive metamorphism

25. Прочитайте текст б и найдите в нем ответы на следующие вопросы:

  1. What is metamorphism?

  2. Why can metamorphic rocks cleave easily?

  3. Why is the study of metamorphic rocks important?

Unit 5 127

ТЕКСТ Б Metamorphic Rocks

The problem discussed concerns metamorphic rocks which compose the third large family of rocks. "Metamorphic" means "changed frop". It shows that the original^ rock has been changed from its primary form to a new one. Being Subjected to, pressure, heat and chemically active fluids beneath the Earth's surface, vari­ous rocks in the Earth's crust rundergo changes in texture, in mineral corhpositioh and structure and are transformed into meta-morphic rocks. The process describeci is called metamorphism.

As is known, metamorphic rocks have been developed from ear­ lier igneous and sedimentary rocks by the action of heat and pressure. ^ Gneisses, mica schists, phyllites, marries, slate, quartz, etc. belong to the 7sarhe group of rocks, ija'yirijj the same mineral cdni- position as granite, gneisses consist chiefly of quartz, orthoclase andl mica^. However uhMe granite, they have a schistose structure. It rtfeans tjjat their constituents are Aisfnbutejdf in bands or layers and rar^ parallel to each other in one'Direction. If 4|sjturbed jhe rock Cleaves easily into separate plates.

The role of water in rnetamorphism is deterrnine^ by at least four v^riaDle'geologically refuted parameters: rock pressure, tempera-

ture .water pressure, and the am'oimt of water present.

? During a normal progressive metamorphism rock pressure and temperature are iriterciependent, and the amount of water and the pressure of water arejrela|e<! ?t^ the sediments and to the degree of metamorphism in'such a^way'tfiat, gerienBry. speaking, the low-grade metamorphic rocks are characterized by the excess of water. The medium-grade rocks defined by some deficiency of water and the high-grade metamorphic rocks are characterized by the absence of water.

Many of the metamorphic rocks -mentioned above consjst,of flaky materials such as mica and chlorite. These minerals cause the' rock to split into thin sheets, and rocks become foliated.сг-оисъи

Slate, phyllite, schist and gneiss belfcng to the group of foliated metamorphic rocks. Marble and quartzite are non-foliated metamor­ phic rocks,

The structure of nietamo,rphic rocks is of importance because it shows the nature of i>re-existmg j;ocks and the mechanism of metamorphic deformation. Every trace ofc/6nginal structure is of great importance to geologists. It gives an opportunity of analysing the causes of its metamorphism.

128 Unit 5

Being often called crystalline schists, metamorphic rocks such asi gneisses and mica have a schistose structure. Metamorphic rocks represent the oldest portion of the Earth's crust. They are mostly found in the regions of mountain belts where great dislocations on the Earth once took place.

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