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TEACHING EARTH SCIENCES ● Volume 31 ● Number 4, 2006 Reviews Inventing the Earth: ideas on Landscape Development Since 1740. by Barbara A.Kennedy. Blackwell Publishing Ltd. Oxford, 2006. 160pp. ISBN-13: 978-1-4051-0187-5 (Hardback), ISBN-10: 1-4051-0188-1(Paperback) In her Preface the author stresses that this is not a text-book on the History of Earth Science, but rather forms a series of essays giving a personal impression of the importance of key episodes in the development of geomorphology within an Anglo- American perspective. Much of the material is drawn from lectures, seminars and tutorials given in the Universities of Manchester and Oxford towards the end of the twentieth century. Nearly one third of the 126 pages of text is devoted to examination of the precepts by which scientific paradigms are tested, exploring the impacts of the Ruling Hypothesis and the Method of Multiple Working Hypotheses. She identifies four key constraints under which the emerging eighteenth century geomorphologists were forced to work. First that the Bible contained Divine Authority, second that the time framework since creation as calculated by Ussher was very limited, third that the only major change to the Earth’s surface since creation was due to the divinely inspired Noachian flood of 2348BC, and fourth that the Almighty followed the laws of Newtonian mechanics. After Buffon (1749) was heavily criticized by theologians for stating that there was a need for an increased timescale to permit landscape development, it was not until the work of Hutton (1785) and later Playfair (1805) who demanded indefinite time scale to permit lithification, erosion and later tilting before further burial by sediments to allow for the development of unconformities. Although initially disputed by Cuvier and Lyell,the latter came to recognise to need for vast periods of time to allow many observed phenomena to develop. Interestingly Darwin (1859) entered the fray, estimating the need for the passage of 300Ma for formation of the topography of the Weald. Later Holmes (1913) estimated the need for 2000Ma and the latest figure of 4550Ma is from Patterson (1953). The third chapter is devoted to the influence of Lyell on developing acceptable ‘modern’ scientific methods of assessing the main elements of geology in the nineteenth century. To the British geologist/ geopmorphologist the in-depth assessment of the contributions of French, German, Italian and Swiss workers gives a welcome historical context, for any advances in the science must be seen within the framework of knowledge of the time. Conflicting views of the presence of polymict gravels between lava flows and their relationship to the biblical deluge or repeated catastrophic events are presented with valuable comments. The need for mechanisms to produce landforms and their distributions is introduced with questions such as ‘Are the highest mountains the oldest or the youngest?’ Kennedy points out development of concepts through the eleven editions of Lyell’s Principles of Geology which provide insights into active processes. Although essentially uniformitarian at heart, Lyell collected evidence of earthquake impacts and sea-level changes as at Serapis. It is instructive to learn that Lyell not only identified that climate change in one area was accompanied by climate change elsewhere, but also believed that the distribution of mountain ranges also exerted some controls on climate. The fourth chapter opens with a list of factors by which Huttonian concepts failed to satisfy conditions in many upland areas. In the Alps both Charpentier and Saussure had identified such problems before Agassiz provided his comprehensive analysis of glacial phenomena, suggesting interpretations which Lyell initially found difficult to accept, but later espoused. The fifth chapter addresses advances resulting from the increasing possibility of scientists taking part in the major exploratory expeditions, of which Darwin on the Beagle is perhaps the most familiar example. Although armed with a copy of Lyell, Darwin made his own observations of geomorphological processes and products in many areas. His original contributions in the study of coral reefs, volcanic islands, and extensive geological observations along the coasts of south America have been highly praised. His genius would have been recognised for those works alone irrespective of his evolutionary concepts. It took over 180 years of investigation before it was accepted that rain and rivers are important in earth sculpture, with wind, ice and the sea playing minor or local supporting roles on landscape development. Outside Europe, until the end of the American Civil War, virtually only the landscapes of the north and north-east of America had been examined. From his observations on the U.S. Government Expedition of 1838-43 Dana believed that all major river systems were post-Tertiary in origin, largely on the basis of rapid fluvial incision into Pacific volcanic islands. In terms of landscape development Kennedy identifies the problem facing these geomorphologists, namely how a narrow gorge or steep-sided valley could open up to a shallow cross-section with gently inclined slopes. It was the pioneering work of Powell in the Grand Canyon which showed the connection between vertical and horizontal denudation. His inspirational recognition of the base level concept linked uplift to valley development and the role of tectonism in stimulating subaerial denudation. Elevation above base level, induration of the rocks, and the amount of rainfall were identified as principal factors, with vegetation cover a further contributor. Like Gilbert, later, www.esta-uk.org 36
TEACHING EARTH SCIENCES ● Volume 31 ● Number 4, 2006 Powell was promoted to an administrative position, which effectively curtailed his scientific contributions. Gilbert, the precursor of physical reductionism, applied Newtonian principles in his monumental works on the Henry Mountains and Lake Bonneville. He linked stream gradient and the loads carried, recognising that equilibrium conditions could be reached, noting that steeper slopes erode more rapidly than gentle ones, divides migrating towards the flatter stream. Three channel forms were identified, alluvial, rock-walled, and rock bound, to which Kennedy adds rock-floored. An advocate of the multiple hypothesis method, Gilbert was fully prepared to discard ideas shown to be untenable, a striking contrast to the approach of many later workers. The genius of W.M. Davis is explored in Chapter seven. A great traveller he was a prolific writer, but unlike Gilbert, he sharply opposed any critical analysis of his ideas. Kennedy draws attention to the dynasty of several generations of researchers who derived early stimulus from Davis, his students or their students. While others were cataloging landform types and processes, Davis provided the concept of progressive change, from youthful through maturity to old age conditions for landscapes formed under differing conditions. His syntheses gave frameworks into which the work of others could be fitted. However forward-looking, his imaginative denudation chronology scheme is almost impossible to test. While Davisian theory was largely developed for river systems dominated by vertical erosion following uplift, alternative views were developed by workers operating in other climatic or structural situations, notably in Africa. Penck believed that tectonic influences were of over-riding importance, and King, who demonstrated landscapes based on the retreat of escarpments in southern and eastern Africa, rejected Davisian concepts as ‘cerebral analysis rather than from observation’. Kennedy sees the Davis approach as an ‘episode’ which attracted many early supporters, but is now seen to have had many failures. Chapters eight and nine are devoted to the post-1945 period during which the advent of plate tectonics, climate change and absolute age dating have all shed previously unsuspected light, requiring re-evaluation of many earlier geomorphological concepts. The quantitative revolution introduced by Horton, and an ever-increasing leaning towards hydraulic analysis of river flow and sediment transport opened fresh directions for geomorphological investigators. While Horton achieved whole landscape evolution analysis by numbering streams according to their relative size and location, modification by Strahler was provided by Strahler. The combination of statistical and mathematical analysis stressed by Strahler was followed through by Morisawa, while another of his students, Schumm devoted his attention to the relative importance of runoff and infiltration in the dissection process. The more Newtonian directions were followed by Leopold, who stressed the importance of using engineering approaches to discriminate between processes leading to braiding or meandering reaches of rivers, albeit, primarily in the south-west of the United States. Although the Leopold methods of analysis are currently most widely in use today, he rates only 33 lines of text compared with more then three pages devoted to Strahler and his immediate students. Beyond the attempts to establish methods of predicting return periods of storm and flooding events many of the more recent advances are dismissed as reductionist attempts to simplify processes into a series of regression equations. In the final chapter Barbara Kennedy allows herself a little flexibility to point out that strictly uniformitarian principles operate on geological rather than human time scales, so that significant natural catastrophes are, by definition, rare events. Having referred to Krakatoa, San Francisco, Pinatubo, Kobe, Bangladeshi floods and Mt St Helens she returns to the concept that the most impactful events on landscape development are probably those recurring at two to three year intervals. After a brief reference to the possibilities opened up by analysis using fractal based, scale-free analysis the text is concluded with the statement that perhaps the earth responds to a different suite of largely mechanical endogenetic and exogenetic forces than those we have hitherto assumed as dominant. After a brief epilogue the text closes with thumb-nail sketches of the many prominent geomorphologists referred to, with a valuable glossary and a useful list of mainly accessible references. The author is to be congratulated on packing so much thoughtful detail into such a brief account. The text is not merely an extended geomorphologistology, but plots the sequences of advances of thought, taking into account what had preceded the development of the ideas. The closely written text is extremely informative and bears all the hallmarks of a thoroughly researched piece of work. I would have no hesitation in recommending it to students intending to follow geomorphology within degree level studies, but would be cautious of letting junior students loose on it until they had already acquired some background within geomorphology, whether from geographical or geological backgrounds. The work is well illustrated with relatively few wood-cuts, but the author must be disappointed with the quality of Blackwell’s reproduction of the photographs seen in the soft-back edition. This is the only unfavourable comment which I would make on what was a very good and thought-provoking read. John McManus University of St Andrews 37 www.esta-uk.org
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