---
title: "Primary versus secondary geological structures"
subject: "Engineering Geology I"
chapter: 5
key: "semester_3/engineering_geology_i:primary-versus-secondary-geological-structures"
source: https://www.bctengineer.com/q/semester_3/engineering_geology_i/primary-versus-secondary-geological-structures
site: BCT Engineering
---

# Primary versus secondary geological structures

Engineering Geology I · Chapter 5: Structural Geology

- Asked in: 2081 Baisakh (new course), 2 marks; 2081 Bhadra, 2 marks; 2076 Chaitra, 2 marks; 2068 Chaitra, 5 marks (asked 4 times)
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_3/engineering_geology_i/primary-versus-secondary-geological-structures
- Whole chapter: https://www.bctengineer.com/md/semester_3/engineering_geology_i/chapter-5

## Question

Differentiate between primary and secondary geological structures.

## Short answer

Primary structures like bedding form during rock genesis, while secondary structures such as folds and faults develop later from tectonic stresses. Primary structures indicate original environment; secondary ones reflect deformation history and create weakness zones.

## Answer

| Point | Primary structures | Secondary structures |
|---|---|---|
| Time of formation | Formed during or at the time of rock formation | Formed after the rock formation, by later deformation |
| Cause | Deposition, cooling, or flow of magma | Tectonic stresses (compression, tension, shear) |
| Examples | Bedding, cross bedding, ripple marks, mud cracks (sedimentary); vesicles, flow banding, columnar jointing (igneous) | Folds, faults, joints, cleavage, foliation, lineation, unconformity |
| Rocks | Mostly igneous and sedimentary rocks | Seen in all rocks, mainly sedimentary and metamorphic rocks |
| Use | Show the original environment and way up of beds (top/bottom) | Show the deformation history and stress direction |
| Engineering effect | Give planes of weakness like bedding | Cause weak zones, leakage, instability: faults, joints |

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. Primary structures form when?
   A. During rock formation
   B. After by tectonics
   C. During weathering
   D. During erosion
   Answer: A. Secondary form later. (Key point: Time)

2. Which is primary?
   A. Fault
   B. Ripple marks
   C. Fold
   D. Cleavage
   Answer: B. Sedimentary. (Key point: Examples primary)

3. Which is secondary?
   A. Mud cracks
   B. Vesicles
   C. Joints
   D. Cross bedding
   Answer: C. Tectonic. (Key point: Examples secondary)

4. Primary structures show what?
   A. Stress direction only
   B. Fault age
   C. Metamorphic grade
   D. Original environment and way up of beds
   Answer: D. Top/bottom. (Key point: Use)

## Related in Engineering Geology I

- [Primary and secondary structures; strike and dip](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Aprimary-and-secondary-structures-strike) — Engineering Geology I, chapter 5, asked 2×

## Related in other subjects

- [Primary and secondary energy at 45% exceedance](https://www.bctengineer.com/question.md?key=semester_6%2Fhydro_power%3Aprimary-secondary-energy-45pct) — Hydro Power, chapter 3
- [Primary and secondary energy (102 m head)](https://www.bctengineer.com/question.md?key=semester_6%2Fhydro_power%3Aprimary-secondary-energy-102m) — Hydro Power, chapter 3
- [Primary/secondary energy and pondage volume](https://www.bctengineer.com/question.md?key=semester_6%2Fhydro_power%3Aenergy-and-pondage-volume) — Hydro Power, chapter 3
- [Primary and secondary energy with 10% environmental flow](https://www.bctengineer.com/question.md?key=semester_6%2Fhydro_power%3Aenergy-with-environmental-flow-950) — Hydro Power, chapter 3