This document defines and describes the key elements and terms related to rock folding. It begins with an introduction stating that folding occurs when rock strata bend due to compressional forces, forming undulating waves on the earth's surface known as folds. It then discusses the historical development and definitions of folding terminology put forth by early geologists. The main body defines elements of folds such as hinge points, limbs, anticlines, and synclines. It concludes by noting that folding is important because it brings minerals closer to the surface and can lead to earthquakes during fault development.

1. Guided By Presented By
Dr. Poonam Bhatnagar Jaya Pandey
Class-M.Sc.(I Sem.)
Govt. Holkar Science College, Indore(M.P.)
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2. CONTENT
Introduction
Historical Development
Elements of Fold
Conclusion
Reference
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3. INTRODUCTION
 The bending of rock-strata due to compressional
forces acting tangentially towards a common point or
plane from opposite directions is known as folding. It
results in the crumbling of strata, forming wavy
undulations on the surface of the earth, which are
known as folds.
 Folds are best displayed by stratified formations.
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5. HISTORICAL DEVELOPMENT
 The word fold was used by HALL(1815) for the first
time to explain the rock structure.
 VAN HISE(1894) contributed on the geometry of
folds.
 WILLIS(18910) worked out their mechanics.
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6. ELEMENTS OF FOLD
Hinge point:- Point located at the maximum
curvature.
Hinge line:- A line joining hinge point.
Hinge zone:- Region on the folded surface
near hinge line.
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8. Enveloping surface:- The enveloping surface
is the surface tangent to individual hings along a
folded layer.
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9. Crest point:- Point located at maximum height of
the folded layer with reference to a horizontal
reference plane.
Crest line:- A line joining successive crest point.
Crestal plane:- P There is a separate crest for
each bed. The plane or surface formed by all the
crests is called the crestal plane.
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11. Trough:- A point located at minimum height with
reference to horizontal reference plane.
Trough line:- A line joining point of minimum
height.
Trough plane:- The trough is the line occupying
the lowest part of the fold. The plane containing
such lines may be called the trough plane.
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13. Culmination point:- The culmination also
refers to the highest point along any geologic
structure.
Depression point:- Point where the trough line
reaches its minimum elevation.
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14. Core:- The inner part of the fold.
Envelop:- Outer part of the fold.
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15. Wavelength of fold:- Distance between two
continuous anticline or syncline.
Amplitude of fold:- Distance between
maximum or minimum height to median surface.
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16. Inflexion point:- The inflexion point of a fold is
the point on a limb at which the concavity reverses;
on regular folds, this is the midpoint of the limb.
Inflexion line:- A line joining such points on a
folded surface is called inflexion line.
Inflexion surface:- A surface joining succession
inflexion lines in different layer within a single fold
and defines the limit of a fold in 3-dimensions.
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18. Limbs:- Limbs are the sides of a fold. An individual
fold will have two limbs ; whereas, in a series of folds,
the central limb is common to any two adjacent
folds.
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19. Interlimb angle:- The smaller angle made by the
limbs of fold is known as the interlimb angle.
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20. Fold axis:- An imaginary line in space along which
the fold is generated. It does not have a fixed position
on the folded surface unlike the hinge.
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21. Axial plane:- Axial plane is the imaginary plane
bisecting between the two limbs of a fold, thus
dividing the fold into two parts, as symmetrically
as possible. Axial plane may be vertical, inclined,
or even horizontal.
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22. Axial surface:- The surface containing the hinge
lines from consecutive folded surfaces.
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24. Anticline:- When the beds are up-folded into an
arch-like structure, it is called anticline or an
anticline fold.
Syncline:- When the beds are down-folded into a
trough like form, the structure is called a syncline,
because in this case the beds on either side “inclined
together’’ towards the keel.
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26. CONCLUSION
 Fold is very important structure. Folding bring
minerals like copper & lead closer to the surface
making their extraction easy.
 Fold mountain receives heavy rainfall giving rise
to rivers which are use for hydroelectric power
generation.
 During folding faults develops leading to
earthquake. 26

27. REFERENCE
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28. THANK YOU
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