Page 30 - 4571

magma generated fissures in the volcanic cone out of which lava flowed. In many
respects, sills closely resemble buried lava flows. Both are tabular and can have a wide
aerial extent, and both may exhibit columnar jointing.

Task 3. Answer the following questions, using the vocabulary from Task 1.
1. What is host or country rock?
2. What is the name of the structures that result from the emplacement of magma
into pre-existing rocks?
3. Do intrusions occur in a great variety of sizes and shapes?
4. What shape do some plutons have?
5. What differences influence the classification of intrusive igneous bodies?
6. What igneous bodies are said to be discordant? concordant?
7. When are tabular intrusive bodies produced?
8. What is a dike?
9. What is a sill?
10. What is a difference between a dike and a sill?
11. What is a dike swarm?
12. What tendency do dike swarms reflect?

Task 4. Look at Figure 5.1A, B and C. Figure A shows Salt River Canyon,
Arizona. The dark, essentially horizontal band is a sill of basaltic composition that
intruded horizontal layers of sedimentary rock. Figure B shows the vertical structure
that looks like a stone wall - a dike, which is more resistant to weathering than the
surrounding rock. This dike is located west of Granby, Colorado, near Arapaho National
Forest. Figure C depicts columnar jointing in basalt, Giants Causeway National Park,
Northern Ireland. These five-to seven-sided columns are produced by contraction and
fracturing that result as a lava flow or sill gradually cools. Using the information from
the text, compare the sill, the dike and the columnar jointing.

Task 5. Find English equivalents for the following (see the text). Try to
build up your own sentences with them.
Підніматись вверх скрізь земну гору; основна або місцева гірська порода;
досягнути поверхні землі; кристалізуватись на глибині; велике різноманіття
розмірів та форм; пластова або плитоподібна форма; включати в себе існуючі
структури; вводитись між шарами осадових порід; примусово вводитись у розлом
або тріщину; використовувати слабкі місця між осадовими шарами; служити у
якості пластових або плитоподібних трубопроводів; транспортувати магму;
зберігати магму; відображати тенденцію формування групових розломів; спиці
колеса; бути дуже схожим на підземні потоки лави.

Task 6. Give a short summary of the text from Task 2.

Grammar focus

The Present Indefinite and the Past Indefinite Tenses

Task 1. Read the sentences. Find the verbs, tell what grammar tense they
are used in. Build up a negative form, a general and a special question to each
sentence according to the model:
Model: The study of various Earth materials provides insights into many basic
processes.

29