This document discusses several theories of mountain building: 1. The geosyncline orogen theory of Kober proposes that mountains form in mobile zones called geosynclines that are surrounded by rigid land masses and subjected to contraction forces from Earth's cooling. 2. Jeffreys' thermal contraction theory attributes mountain-building forces to cooling of the Earth and slowing of its rotation. This explains the perpendicular orientation of mountains to continental margins. 3. Joly's radioactive theory proposes that heat from radioactive elements in the crust causes expansion and contraction cycles leading to deposition of sediments in geosynclines that are later compressed into mountains. 4. Daly proposed that gravity drives downhill sliding of continental masses. Holmes suggested

1. MOUNTAIN BUILDING
THEORY
Bhagyashri

2. GEOSYNCLINE
 LONG, NARROW, SHALLOW DIPRESSIONS OF WATER.
 CHARACTERIZED BY GRADUAL SEDIMENTATION AND SUBSISDENCES.
 LOCATION, SHAPE, DIMENSION, AND EXTENT OF GEOSYNCLINE IS CONSIDERABLY
CHANGED DUE TO EARTH MOVEMENT AND GEOLOGICAL PROCESS.
 MOBILE ZONE OF WATER
 GEOSYCLINE ARE BORDERED BY TWO RIGID MASSES

3. STAGES OF GEOSYNCLINES
 DIVIDED INTO THREE STAGES:
 LITHOGENSIS: STAGE OF CREATION OF GEOSYNCLINES, SEDIMENTATION
AND SUBSIDENCE OF THE BEDS OF GEOSYNCLINE.
 OROGENESIS: THE STAGE OF SQUEEZING AND FOLDING OF GEOSYNCLINE
SEDIMENTS INTO MOUNTAIN RANGES.
 GLIPTOGENESIS: THE STAGE OF GRADUL RISE OF MOUNTAINS, AND THEIR
DENUDATION AND CONSEQUENTT LOWERING OF THEIR HIEGHTS

4. THEORIES OF MOUNTAIN BUILDING
 GEOSYNCLINE OROGEN THEORRY OF KOBER:
 OBJECTIVE OF THEORY:
To establish relationship between ancient rigid masses or tablelands and more
mobile zones or geosynclines, which he called orogen.
 OROGENETIC FORCE:
Theory is based on the force of contraction produced by the cooling of the earth.

5. BASE OF THE THEORY
 Mobile zones of water : geosynclines or orogen (the place of mountain building).
 These mobile zones of geosynclines were surrounded by rigid masses which
were termed by Kober as kratogen / Foreland.
 This unfolded middle portion is called zwischengebirge.
 MARGINAL RANGE: Randketten

8. THERMAL CONTRACTION THEORY OF JEFFERY’S
Orogenetic forces:
1. forces coming through the COOLING
OF THE EARTH
2. forces coming through the decrease
in the SPEED OF EARTH’S ROTATION

9. THERMAL CONTRACTION THEORY OF JEFFERY’S

10. SHORTNING OF EARTH AND LEVEL OF NO STRAIN

11. DIRECTION OF MOUNTAINS
 Compressive force generated by contraction of earth directed from oceanic areas
towards continental areas almost at right angle.
 Thus mountains are formed parallel to the continent margins.
 Solved the north-south direction of rockies and Andes.

13. RADIOACTIVE THEORY OF JOLY
 The driving force of the mountain building as invoked by Joly is provided by
expansion and contraction of the substratum of the earth resulting into
transgressional and regressional phases of the seas (geosynclines).
 The expansion and contraction of the substratum are based on the mechanism of
heat generated by radioactive elements of the rocks.
 Holmes used radioactive elements to explain the origin of thermal convective
currents in the substratum while Joly used them to explain the melting and re-
solidification of the substratum.

14. RADIOACTIVE THEORY OF JOLY
 continents are made of lighter sialic materials the density of which is 2.67 while
the oceanic beds are formed of heavier materials of sima having average density
of 3.0.
 Rocks of the earth contain radioactive elements but their distribution is not uni-
form in all zones of the earth.
 Radioactive elements are found in abundance in the continental rocks
 The rocks of sima forming the oceanic crusts are less radioactive.

15.  Production of heat is comparatively higher in the continental crust because of
more radioactive elements than the oceanic beds.
 There is no large-scale accumulation of heat in the continental crust due to
continuous loss of heat through radiation.
 Retention of heat below SIMA due to radioactivity and lack of thermal gradient
b/w SIMA and SIAL
 Melting -> Expansion

16. Melting of Substratum -> Max Expansion –
Transgressional Sea
Re-solidification of Substratum -> Max
Contraction – Regressional Sea

18. CONCLUSION
 Thus, contracting beds of two oceans exert
lateral compression on the sediments deposited
on the continental margins (geosynclines),
consequently the sediments deposited during
the period of transgressional sea are squeezed,
buckled and folded and thus mountains are
formed.

19. Continent Sliding Hypothesis of Mountain Building of Daly
 The main force implied by Daly: the force of gravity
 there has been downhill sliding movement of continental masses.

21. Thermal Convection Currents by Arthur Holmes