---
title: "Classification of folds"
subject: "Engineering Geology I"
chapter: 5
key: "semester_3/engineering_geology_i:classification-of-folds"
source: https://www.bctengineer.com/q/semester_3/engineering_geology_i/classification-of-folds
site: BCT Engineering
---

# Classification of folds

Engineering Geology I · Chapter 5: Structural Geology

- Asked in: 2078 Kartik, 2 marks; 2076 Chaitra, 2 marks (asked 2 times)
- Video: [Classification of Folds](https://www.youtube.com/watch?v=_7saYFzkIKs) — Angie Allison
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_3/engineering_geology_i/classification-of-folds
- Whole chapter: https://www.bctengineer.com/md/semester_3/engineering_geology_i/chapter-5

## Question

Describe the classification of folds (on the basis of convexity / position of axial plane).

## Short answer

Based on convexity: anticline (arches upward), syncline (trough), monocline (step). Based on axial plane: symmetrical (vertical), asymmetrical, overturned (both limbs dip same way), recumbent (horizontal), isoclinal (parallel limbs).

## Answer

Folds are classified on several bases. The two bases mentioned are explained here.

#### On the basis of convexity (upward or downward)
1. **Anticline** - an upward arch; limbs dip away from the axis and older beds are in the core.
2. **Syncline** - a downward trough; limbs dip towards the axis and younger beds are in the core.
3. **Monocline** - a local steepening in otherwise gently dipping beds, a single step.

#### On the basis of position of the axial plane
| Fold | Axial plane | Limbs |
|---|---|---|
| **Symmetrical (upright)** | Vertical | Dip at equal angles in opposite directions |
| **Asymmetrical** | Inclined | Dip at unequal angles |
| **Overturned** | Inclined strongly | Both limbs dip in the same direction, one limb inverted |
| **Recumbent** | Horizontal (or nearly) | Limbs lie horizontal, one above the other |
| **Isoclinal** | Any | Limbs parallel to each other |

```text
 Symmetrical   Asymmetrical   Overturned   Recumbent
    /\             /\           /\          ____
   /  \           /  \         /  \_       /____\_
  /    \         /    \       /  /  /      \_____/
 vertical axial  inclined    both limbs     horizontal
 plane           axial       dip same way   axial plane
```

Other bases: plunge (plunging, non-plunging), shape (chevron, box, conical).

## Check yourself

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

1. Anticline limbs dip?
   A. Towards
   B. Parallel
   C. Away from axis
   D. Same direction
   Answer: C. Older core. (Key point: Anticline)

2. Recumbent fold axial plane?
   A. Vertical
   B. Inclined
   C. Curved
   D. Horizontal
   Answer: D. Limbs one above other. (Key point: Recumbent)

3. Isoclinal limbs?
   A. Parallel to each other
   B. Opposite equal
   C. Horizontal
   D. Unequal
   Answer: A. Any axial plane. (Key point: Isoclinal)

4. Symmetrical fold axial plane?
   A. Horizontal
   B. Vertical
   C. Inclined
   D. None
   Answer: B. Equal dips. (Key point: Symmetrical)

## Related in other subjects

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- [Masonry pier under axial load and in-plane moment](https://www.bctengineer.com/question.md?key=semester_5%2Fdesign_of_timber_and_masonry_structures%3Amasonry-pier-axial-moment-check) — Design of Timber and Masonry Structures, chapter 7
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- [Material classification, EOQ, GiT and re-order level](https://www.bctengineer.com/question.md?key=semester_8%2Fconstruction_management%3Aclassification-eoq-gitt-2079) — Construction Management, chapter 3