Geology and Landscapes of Scotland: Second Edition

256 Pages·2013·28.432 MB·English

by  Con Gillen

G
Con Gillen
The six hundred miles between the northernmost Shetland e
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island and the Mull of Galloway in the south of Scotland
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contain some of the most interesting geology and most varied
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landscapes in Europe. This variety was the inspiration for a y
tradition of geological investigation that stretches back to the Geology and landscapes
a
earliest earth scientists. n
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The origins of the Scotland that we know today lie in five
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quite distinct geological histories. Geology and landscapes of a
of Scotland
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Scotland takes the reader on a tour of each of these regions
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in turn, starting with the Northwest Highlands and Outer s
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Hebrides, which contain some of the oldest rocks in Europe,
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through the mountain terrains of the Highlands and Uplands p Second Edition
to the Lowlands and then the fringes of the North Sea. A e
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section describes the volcanic provinces of Scotland; another

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deals with the effects of the Ice Ages while a final section
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looks at Scotland’s natural resources. S
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Of equal appeal to the professional geologist seeking a
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broad overview of a much-studied terrain and a resource for t
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the resident, visitor, walker, climber or angler who wants a
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to understand the origins of the landforms they observe,
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Geology and landscapes of Scotland has proved itself as a
reliable guide. In this thoroughly revised edition the many
illustrations are presented in colour. G
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Con Gillen is an experienced geologist, now with the l
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University of Edinburgh, who has led many field trips across e
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the country. Much of his teaching has been devoted to
introducing geology to those new to the subject.
Cover photograph: Loch Coruisk, below the Cuillin complex on the Isle of Skye (by permission of Shutterstock, © N Mrtgh)
ISBN: 9781780460093
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D
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DUNEDIN
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EDINBURGH  LONDON N
Geology and landscapes of Scotland
Iona, looking toward the Ross of Mull granite (pink), with Ben More and lava flows behind. Rocky knolls on Iona are Lewisian gneiss.

Geology and
landscapes
of Scotland
Second edition
Con Gillen
University of Edinburgh
DUNEDIN
EDINBURGH  LONDON
[[title page verso]]
First edition published by Roger Jones,
Terra Publishing, Harpenden, UK in 2003
Second edition first published in 2013 by
Dunedin Academic Press Ltd
Head Office:
Hudson House, 8 Albany Street,
Edinburgh EH1 3QB
London Office:
The Towers, 54 Vartry Road,
London N15 6PU
See www.dunedinacademicpress.co.uk for all our publications
in Geology and the Earth Sciences
ISBN 978-1-78046-009-3
© 2013 Cornelius Gillen
The right of Con Gillen to be identified as the author of this book has been asserted by him in
accordance with sections 77 & 78 of the Copyright, Designs and Patents Act 1988
All rights reserved.
No part of this publication may be reproduced or transmitted in any form or by any means or stored
in any retrieval system of any nature without prior written permission, except for fair dealing under
the Copyright, Designs and Patents Act 1988 or in accordance with a licence issued by the publisher
or the Copyright Licensing Society in respect of photocopying or reprographic reproduction. Full
acknowledgment as to author, publisher and source must be given. Application for permission for any
other use of copyright material should be made in writing to the publisher.
British Library Cataloguing in Publication Data
A catalogue record for this book is available from the British Library
Typeset by Makar Publishing Production, Edinburgh
Printed in Poland by Hussar Books
Contents
Contents
Prefaces and acknowledgements vii
1. Geology – the science of the Earth 1
Introduction 1
The rock fabric of Scotland 1
The rock cycle 12
Structure of the Earth 12
Folds, faults and shear zones 15
Time and life 19
2. Geological regions of Scotland 26
Introduction 26
Geological regions 27
Geological evolution 30
What next? 38
3. Scotland’s oldest rocks – the far northwest 40
Introduction 40
The Northwest Highlands 42
The Outer Hebrides 61
Basement rocks of the Inner Hebrides 64
4. The Caledonian Mountains 67
Introduction 67
The Northern Highlands 73
The Grampian Highlands 77
Igneous rocks in the Caledonian Mountains 88
The Highland Border Complex 90
Geology of Shetland 91
The Southern Uplands 96
Plate tectonics and drifting continents 105
5. Lowland Scotland: after the mountains 109
Introduction 109
Ordovician and Silurian rocks 110
Devonian rocks 111
Scotland in the Carboniferous 119
v
vi Contents
6. The North Sea and the Inner Hebrides 128
Introduction 128
New Red Sandstone 128
Tropical seas of the Jurassic 132
Chalk seas of the Cretaceous Period 136
7. Hebridean volcanoes 138
Introduction 138
The Small Isles 143
Skye 148
Mull 154
Ardnamurchan 156
Arran and Ailsa Craig 158
St Kilda and Rockall 160
Dyke swarms 161
Landscape evolution 163
8. Ice Age Scotland 165
Introduction 165
The cooling climate 165
Causes of ice ages 166
Landforms created by glacial erosion 169
Landforms created by glacial deposition 176
Postglacial landscapes and sea-level changes 181
9. Natural resources, people and landscape 186
Introduction – what is a natural resource? 186
Metal-ore deposits 186
Industrial materials 191
Fossil fuels 200
Alternative energy sources 205
Resources and the landscape 206
Summary – resources through time 207
People and the landscape 207
Appendix 211
Taking it further / Fieldwork / Geological maps 211
Glossary of technical terms 213
Gaelic terms 229
Bibliography 230
Index of place names 232
General Index 236
Prefaces and acknowledgement
Prefaces and acknowledgements
Preface to the first edition Preface to the second edition
Scotland has been a Mecca for geologists for over two In the ten years since the first edition was written,
centuries. Indeed, the subject of geology was born here, Scotland has remained at the forefront of geological
with the pioneering work of the great James Hutton in research, and many of the pioneering ideas have been
the 1780s and, ever since, Scotland has played a key role put to the test using new age-dating techniques, which
in the development of ideas in geology. And with good are becoming ever more sophisticated and accurate. This
reason, for Scotland boasts the most varied geological has resulted in some of the earlier ideas being challenged,
tapestry of any country of its size in the world. with new interpretations put forward. Paradoxically, the
This book has been designed for non-expert readers, recent results more often than not show the need to apply
and has been written in such a way that all the key the new techniques to more of the country as further
concepts in geology are explained in a jargon-free and problems are brought to light. Great strides have been
approachable way. The book presents an up-to-date made in studying the age and structure of the Caledonian
account of each of Scotland’s unique geological regions, Mountains for example, yet still there are challenges in
from Shetland and Orkney, through the Western Isles to finding the age and extent of the Dalradian rocks. For
the Highlands, Central Lowlands and Southern Uplands. over two centuries, Scotland has been a natural geologi-
We trace Scotland’s movements across the globe from the cal field laboratory, and it is gratifying to think that it
dawn of time – how we moved from southern ice-bound looks set to remain as one of the world’s foremost outdoor
seas across the Equator into warm, humid coal-forming laboratories for years to come. International conferences
swamps, to be confronted eventually by icy conditions, are regularly held here, and always accompanied by field
this time near the North Pole. The book deals not just trips to classic sites.
with the wide variety of rocks (and the minerals and fossil Have you ever stood on the shore at Achmelvich in the
remains they contain), but also the landforms and scenic Northwest Highlands and looked across at Lochinver,
types that owe their origin to the structure and compo- wondering how that great sugarloaf mountain of Suilven
sition of the bedrock. We explore how these landforms came to be? This book will provide the answer to that and
developed through time, to be used to great advantage many other questions that fascinate the visitor attracted
by Scotland’s first settlers, and how the mineral riches by Scotland’s spectacular scenery, whether you are a
have been exploited, from iron ores and building stones walker, climber, archaeologist or rock collector. The
to coal, oil and gas. great pioneers of Scottish geology will be introduced,
Many of the fundamental ideas in geology were including James Hutton (1726–97), who is regarded as
developed on the basis of rocks and structures seen in the founder of modern geology and the discoverer of
Scotland. Indeed, Scotland could justifiably be called ‘deep time’.
the cradle of modern geology. For its relatively small Thanks to the way Scotland developed over 3 billion
size, the country boasts a truly amazing variety of rocks years of Earth history, it is possible to divide the country
and structures. At first sight, this may appear daunting into five quite separate regions, each with its own distinc-
and even confusing to the novice, but Geology and land- tive age, history and rock types. This book will take you
scapes of Scotland will put you at your ease and allow on a journey through the five regions, starting with the
you to grapple with the most complex of notions, as you incredibly old Northwest Highlands and Outer Hebrides,
travel on a journey, following Scotland’s fortunes in time then the Caledonian Mountain terranes of the Northern
and space. and Grampian Highlands, Argyll, Shetland and the
vii
viii Prefaces and acknowledgements
Southern Uplands. The geology of lowland Scotland is comprehensive glossary of all technical terms used in
visited next – the Midland Valley, Orkney and Caithness, the book is included, and there is a brief bibliography of
and the fringes of the Moray Firth. A return visit is then work, much of which has been published since the first
paid to the west coast, this time to explore the awe-inspir- edition. There is also a list of useful websites.
ing geology of the Hebrides – volcanic mountain land-
scapes of 60 million years ago that heralded the opening
of the North Atlantic Ocean. Finally, we examine the Acknowledgements
effects of the last great Ice Age – one of many in the past I wish to express my gratitude to the late Roger Jones of
– and see how and why the climate cooled rapidly, how Terra Publishing for his unstinting support, professional
the landscape was sculpted by the force of moving ice advice and expertise shown at every stage of production
sheets, and what the future climate may hold in store for of the first edition, from the initial idea to the finished
us. Scotland has rich useful resources of natural materi- work. He also encouraged me to get started on the second
als, from building stones to metal ores and fossil fuels. edition. After Roger’s untimely death, Anthony Kinahan
These are dealt with comprehensively and in context – of Dunedin Academic Press Ltd stepped in admirably,
both regional and in the appropriate geological setting and has done a first class job with the second edition. I
of how, why, when and where they formed. The human also wish to thank my students who, with their stimu-
impact on the environment and the landscape is touched lating questions and bubbling enthusiasm in the field,
upon also. the laboratory and the classroom over the years have
How to use this book? If you have studied geology inspired me to write down my explanations for the fasci-
before, then you may want to skip Chapter 1 and move nating geological history of Scotland. In addition, I am
straight into the regional chapters that are of most inter- grateful to my geological friends for leading me on many
est, moving back to Chapter 1 and the Glossary whenever excursions and discussing their ideas so freely, and for
there is a need to brush up on a particular concept or allowing me to use some of their photographs. Dr Colin
some unfamiliar term. However, if you are new to the MacFadyen and Professor John Gordon very kindly made
subject, then it is advisable to start at the beginning, many helpful comments on the second edition, and I am
by reading Chapters 1 and 2 before moving ahead. A greatly indebted to them for their time and expertise.
Credits
Title page ~ Eilean Donan Castle, shuttterstock © Andre Goncalves; Fig. 1.6 Graham Park; 1.15 Nigel Trewin; 3.11, 3.15,
8.17 the late Roger Jones; 4.14, 7.30 Tim Harrison; 4.10, 4.20, 5.8, 7.15, 7.17, 8.5, 8.12 the late Bill Brooker; 4.21 the late
Don Omand; 5.9 Fiona McGibbon; 5.12 Jim MacDonald; 6.10 Karen MacCormack; 7.5, 9.2 Russell Thomson; 7.28 Donald
Paterson; 8.6 North of Scotland Hydro Board. Geological sketch maps are redrawn from published sources, including some
based on BGS materials. Tables in Ch. 3 and Ch. 4 are based on materials in Mendum et al. (2009), Stephenson et al. (2013)
and Woodcock & Strachan (2012). Information on mineral deposits in Ch. 4 and Ch. 9 is partly based on materials in Pattrick
& Polya (1993).
Geology – the science of the Earth
Chapter 1
Geology – the science of the Earth
Introduction
This book is about the landscape you will see around you by sharp contrasts in the various parts of the country,
as you travel throughout Scotland. What makes up the particularly between the east and the west.
natural landscape? Its components are part of the natural Why do we see such marked contrasts, between high
environment: rocks, soils, relief, climate and vegetation. rugged mountains in the northwest, flat, high table lands
This natural or physical environment in turn consists of in the northeast, lowlands in Central Scotland, and
closely interrelated systems working in harmony within rolling hills in the Southern Uplands? The answer, as we
cycles of varying duration. The landscape itself is not shall soon see, lies in the nature of the bedrock that was
static, but has been evolving constantly throughout the sculpted by the forces of erosion. In very general terms,
history of the Earth by the interaction of animals, plants Scotland is an upland country, with the oldest rocks in
and physical processes, sometimes gradual, often abrupt the northwest and a land surface that slopes to the east
or catastrophic. And, for at least the past 5000 years, and southeast, towards the North Sea, and is the direc-
humans have played an important part in changing the tion of flow of most of the main rivers. The fabric of the
landscape, at an ever-accelerating pace. Recent climatic rocks has strongly influenced the development of the
change as a result of the enhanced greenhouse effect is landscape, since some rocks are relatively weak and can
thought to be mainly induced by humans, and the future be easily sculpted by erosion, whereas others are much
effects on the landscape could turn out to be profound tougher and more resistant to erosion, so they can form
and possibly irreversible in the scale of our lifetime. prominent landscape features. In some parts of the
Scotland is famous for its varied and attractive country, such as the Northwest Highlands, the variety of
scenery, and for the sharp contrasts between different rock types over a small area is considerable, and the result
parts of the country. These scenic differences derive is a complex pattern of landform features that endows the
from natural forces acting on bedrock geology that is region with a scenic beauty scarcely rivalled in the rest of
extremely varied, given the relatively small size of the Britain or Europe.
country (less than 80 000 km2). We now embark on a
journey of exploration through Scotland, looking at the
variety of landscapes, and discovering the reasons for The rock fabric of Scotland
the patterns we see at the surface. In human terms, the The Earth is made of three concentric shells: the crust,
landscape may seem never changing, save for seacliff mantle and core. For our purposes, the crust and the
collapses, or rockfalls down mountainsides, but over upper part of the mantle are the most important. We live
millions of years, it has been changed profoundly by the on the crust, the thin, outermost shell, which is 35 km
action of rain, ice, waves and wind. In the more distant thick on average in the continents and 7 km under the
past, the rocks of Scotland were formed by processes oceans. Continental mountain chains have thicker crust;
that originated in the Earth’s interior: mountain build- for example, the crust beneath the Himalayas is 85 km
ing, folding of rocks, faulting, earthquakes, volcanic thick. The centre of the Earth lies 6371 km beneath the
eruptions and deep underground intrusions of molten surface.
rock. The Scottish landscape is an intricate set of dif- The three main rock types that make up the Earth’s
ferent landform elements of different ages and origins, crust are referred to as:
resulting from a complex geological fabric and combin- ‹igneous, formed by the cooling of molten material
ing to produce an attractive patchwork, characterized from below the crust
1