UPSC Prelims 2001 Q88: Geography – Physical Geography & Geomorphology
Consider the following statements made about the sedimentary rocks:
I. Sedimentary rocks are formed at Earth’s surface by the hydrological system.
II. The formation of sedimentary rocks involves the weathering of pre - existing rocks.
III. Sedimentary rocks contain fossils.
IV. Sedimentary rocks typically occur in layers.
Which of these statements are correct?
- (a) I and II
- (b) I and IV
- (c) II, III and IV
- (d) I, II, III and IV
Answer: (d) I, II, III and IV
Explanation
Statements about sedimentary rocks
| Statement | Verdict |
|---|---|
| I. Formed at the Earth's surface by the hydrological system | Correct — deposited by water, wind and ice |
| II. Formed from weathering of pre-existing rocks | Correct — fragments are carried and deposited |
| III. Contain fossils | Correct — the only rock type that commonly holds fossils |
| IV. Typically occur in layers | Correct — hence 'stratified rocks' |
All four statements are correct. Sedimentary rocks form at the surface from sediments that come from weathering of older rocks, are laid down in layers, and often preserve fossils. Examples are sandstone, shale and limestone.
Answer: (d) I, II, III and IV.
Why each option is right or wrong
- (a) Incorrect. Statements III and IV are also correct.
- (b) Incorrect. Statements II and III are also correct.
- (c) Incorrect. Statement I is also correct.
- (d) CORRECT. All four statements about sedimentary rocks are correct.
Key point
Sedimentary rocks cover about 75% of the land surface but only about 5% of the crust by volume.
Remember
Sedimentary rocks: weathering, layers, fossils, formed at the surface.
Common mistakes
- Thinking fossils are found in igneous rocks.
- Forgetting that sediments come from weathered older rocks.
- Dropping 'hydrological system' because wind also deposits sediments.
Exam tip
Sedimentary = surface, layers, fossils.
Sources
- NCERT Class XI — Fundamentals of Physical Geography, chapter 'Minerals and Rocks'
- Arthur Holmes — Principles of Physical Geology, chapter on sedimentary rocks