Table Of ContentP< OU >m
160144
The -flowing landscapes of geologic time may be
likened to a tynetoscopepanorama. Thescenes transform
from age to age, as from act to act; seas and plains and
mountains follow and replace each other through time,
as the traveller sees them replace each other in space. . . .
Science demonstrates that mountains are transient forms,
but the eye of man through all his lifetime sees no
change, and his reason is appalled at the thought of
duration so vast that the millenniums of written history
have not recorded the shifting of even one of the fleeting
views whose blendings ma\e the moving picture.
JOSEPH BARRELL
FRANZ JOSEF GLACIER, NEW ZEALAND.
C. A, Cotton, photo.
GEOMORPHOLOGY
An Introduction to the Study ofLandforms
BY
COTTON
C. A.
D.Sc, F.R.S N.Z.
PROFESSOR OF GEOLOGY
VICTORIA UNIVERSITY COLLEGE
\\ELLINGTON, NEW ZEALAND
NEW YORK
JOHN WILEY & SONS, INC.
SIXTH EDITION, REVISED 1952
Copyright
PRINTED IN NEW ZEALAND BY WHITCOMBE AND TOMBS LIMITED
PREFACE
TO THE THIRD EDITION
(1942)
may be regarded as a new and revised edition of
of New Zealand, Part I: Systematic, which was
1922 (reprinted 1926) by the Dominion Museum,
as New Zealand Board of Science and Art Manual
No. 3. ne old Geomorphology, which has been out of print for
some years, has enjoyed a considerable popularity notwithstanding
that a rashly promised sequel which was to present a regional
treatment of New Zealand landforms has failed to appear.
Geomorphology makes its appeal not only to geologists and
geographers but also to all who love Nature and have eyes for the
natural landscape. To geologists the form of the surface is of
interest because landforms result from the operation and interaction
of processes which are active also in the production, transportation,
and deposition of the materials that make rocks. It has a further
interest which transcends this, however, in that it gives access to a
record which is in many cases the only record available of a late
period in the history of the earth very scantily documented by
stratigraphy. Farther back in geological history, indeed, there are
many gaps in the stratigraphical record, erosion intervals marked
by unconformities, the correct interpretation of which can be made
possible only by analogy of buried landscapes with landforms and
landscapes as they exist to-day.
Geography on the other hand, is concerned with the surface of
the earth as the environment of organised beings and notably as
the abode of man. From the geographical point of view, therefore,
geomorphology is concerned with the description of the natural
landscape and the classification and labelling of landforms. For
this reason the science has advanced largely as a development of
the method of "explanatory description" advocated by W. M. Davis.
In the present book the treatment is intentionally Davisian in the
sense that explanation is assumed to be a necessary part of landscape
description.
The presentation of the "normal" cycle is Davisian also; for
Davis's down-wearing theory is accepted in explanation of the
origin of peneplains without reference to alternative hypotheses of
slope retreat.
Elements of Geomorphology
Though not written in the conventional form of a s
the old Geomorphology has been found useful as a
first-year students of geology and geography in the Un
Teachers' Training Colleges; and I venture to belie
revised edition is suitable for use also by pupils in
classes in secondary schools. Abridgement for a first re*
be left to the discretion of teachers, whose predilections, ; ,veu as
the availability of local examples of landforms, must governJthe
choice of matter. I hope it is quite obvious that the book has;!ftpt
been written up to meet the requirements of any examination
syllabus. '-
In this elementary treatment of geomorphology, which attempts
to cover in one small volume a wide field of study, limitation"io>f
space has made it impossible to indicate the sources and authorship
of terms employed in a technical sense (for very few of which 1
admit personal responsibility) or to trace the origin of geomorprfic
doctrines and theories. For some information on such matters, p
;
well as for fuller treatment of some aspects of geomorphology, the
reader is referred to other works, to which the brief list in tWe"
Appendix will serve as an introduction.
I am particularly grateful to all those colleagues and corregj*
pendents who have supplied me with and allowed me to use
illustrative material; and I am no less indebted to the professional
photographers whose keen eye for scenic beauty has so often led
to the production of pictures of the greatest value as illustrations of
landforms. Wherever it has been possible acknowledgment for the
illustrations has been made in credit lines.
I am indebted to the New Zealand Government for permission
to draw on Geomorphology of New Zealand, Part I for portions
of the text and for many of the illustrations.
C. A. COTTON.
CONTENTS
CHAPTER I PAGE
The Crust of the Earth . . .. .. .. 1
Uniformitarianism, 1. Geological Processes, 1. The Material of the
Lithosphere: Rocks, 1. Rock Structures, 5. "Structure" or Terrain, 9.
CHAPTER
II ....
Erosion: The Weathering of Rocks . 10
Erosion, 10. Weathering: the Work of Rain and Associated Agents, 10.
Mechanical Weathering or Rock-breaking, 11. Rock-breaking by Organic
Agencies, 16. Rock-decay, 16. Residual Clay, 18. Spheroidal Weathering,
19. Depth of Weathering, 21.
CHAPTER
III
Erosion: Removal of Rock Debris 22
. .
The Mantle of Waste, 22. Gravity Transportation or Mass Movements:
Landslides, 22. Sohfluction, 28. Soil Creep, 28. Water Transportation, 29.
Earth Pillars, 31. Rivers, 32. Corrasion and Transportation by Running
Water, 34. Chemical Corrosion and Transportation in Solution, 34.
Mechanical Corrasion and Transportation in Suspension, 34. The Quantity
of Waste Transported, 36.
CHAPTER IV
.38
Youth of Rivers . . .
NormalErosion, 38. TheGeomorphicCycle, 39. ConsequentDrainage, 42.
Youth, 42. Young Valleys, 43. Vertical Corrasion, 45. Falls and Rapids,
48. Lakes, 54.
CHAPTER V
Maturity of Rivers and Landscapes . . . . 57
Base-level and Grade, 57. Maturity of Rivers, 59. Graded Reaches, 59.
Dissection of the Upland, 60. DevelopmentofMaster Streams, 63. Coastal
Plains, 64. Insequent Streams, 66. The Law of Equal Declivities, 67.
CHAPTER VI
SubsequentRiversand RiverDiversion . .. .. .. 68
Development of Subsequent Drainage, 68. Local Base-levels, 69. Shifting
ofDivides, 69. Capture,or "RiverPiracy," 71. ChangesfollowingCapture,
73. The Kaiwarra Capture, 74.
Elements of Geomorphology
CHAPTER VII PAGE
.76
Mature Landscapes: Adjustment to Structure . .
Subsequent Erosion on Folded Rocks, 76. Adjustment to Structure, 79.
The Drainage of Mountainous Areas of Folded Rocks, 80. Subsequent
Ridges in Synclinal Positions, 81. Resequent Drainage, 83. Homoclinal
Ridges, 84. Escarpments: their Rapid Retreat, 84. Hogbacks, 86.
Cuestas, 86. Homoclinal Shifting, 89. Mesas and Buttes, 92. Structural
Plateaux, 93. Structural Benches and Terraces, 94.
CHAPTER VIII
TheValleysofMature Rivers . 96
Lateral Corrasion, 96. Widening of Valley Floors, 98. Valley Plains and
Meanders, 100. Cutting-off of Meanders, 101. Narrowed and Cut-off
Spurs, 101. Subsequent Lowlands, 104. Wide Valley Plains, 105. Plains
of Lateral Planation, 106. Unclerfit Rivers, 106.
CHAPTER IX
Subdued Landscapes and "Soil Erosion" . . .110
GradingofSlopes, 110. Serrate and Subdued Summit Forms, 110. Convex
andConcaveSummitand SlopeProfiles, 112. Accelerated SoilErosion, 113.
The Soil-erosion Problem, 116. Soil-depleting Processes, 117. Wind
Erosion, 119. Secondary Effects of Accelerated Erosion, 119. The Remedy
for Accelerated Erosion, 119.
CHAPTER X
Limestone Landscapes 121
Rock Solubility: Erosion by Underground Water, 121. Sinkholes, Caves
and Natural Bridges, 123. Hums, 128. Travertine Falls and Dams, 128.
The Karst or Limestone Cycle, 128.
CHAPTER XI
...
Peneplains . . . 132
Destruction of Relief, 132. Peneplains and Monadnocks, 132. Old-from-
birth Peneplains, 134. Dissected Peneplains, 135. Accordance of Summit
Levels, 138.
CHAPTER XII
Superposed Rivers and Resurrected Landscapes . . 139
Erosion on Compound Structures, 139. Superposed River Courses, 140.
Resurrected Fossil Plains, 143. Tests of Fossil-plain Origin, 149. Inter-
se<i)Ling Peneplains, 150. Dissection of an Undermass by Superposed
Rivers, 151.
